diff --git a/src/Automation.php b/src/Automation.php
index 033a9ee4..e39a30a1 100644
--- a/src/Automation.php
+++ b/src/Automation.php
@@ -225,8 +225,6 @@ public static function create_shipments( $order ) {
 
 			if ( $order_shipment->needs_shipping() ) {
 				if ( $order_shipment->has_auto_packing() ) {
-					$items_to_pack = $order_shipment->get_items_to_pack_left_for_shipping();
-
 					if ( $method = $order_shipment->get_builtin_shipping_method() ) {
 						$packaging_boxes = $method->get_method()->get_available_packaging_boxes();
 					} else {
@@ -239,48 +237,47 @@ public static function create_shipments( $order ) {
 						$packaging_boxes = Helper::get_packaging_boxes( $available_packaging );
 					}
 
-					foreach ( $items_to_pack as $group => $items ) {
-						$packed_boxes = Helper::pack( $items, $packaging_boxes, 'order' );
+					$items        = $order_shipment->get_items_to_pack_left_for_shipping();
+					$packed_boxes = Helper::pack( $items, $packaging_boxes, 'order' );
+
+					foreach ( $packed_boxes as $box ) {
+						$packaging      = $box->getBox();
+						$items          = $box->getItems();
+						$shipment_items = array();
 
-						foreach ( $packed_boxes as $box ) {
-							$packaging      = $box->getBox();
-							$items          = $box->getItems();
-							$shipment_items = array();
+						foreach ( $items as $item ) {
+							$order_item = $item->getItem();
 
-							foreach ( $items as $item ) {
-								$order_item = $item->getItem();
+							if ( ! isset( $shipment_items[ $order_item->get_id() ] ) ) {
+								$shipment_items[ $order_item->get_id() ] = 1;
+							} else {
+								$shipment_items[ $order_item->get_id() ]++;
+							}
+						}
 
-								if ( ! isset( $shipment_items[ $order_item->get_id() ] ) ) {
-									$shipment_items[ $order_item->get_id() ] = 1;
-								} else {
-									$shipment_items[ $order_item->get_id() ]++;
-								}
+						$shipment = wc_gzd_create_shipment(
+							$order_shipment,
+							array(
+								'items' => $shipment_items,
+								'props' => array(
+									'packaging_id' => $packaging->get_id(),
+									'status'       => $shipment_status,
+								),
+							)
+						);
+
+						if ( ! is_wp_error( $shipment ) ) {
+							$order_shipment->add_shipment( $shipment );
+
+							$shipments_created[ $shipment->get_id() ] = $shipment;
+						} else {
+							foreach ( $shipments_created as $id => $shipment_created ) {
+								$shipment_created->delete( true );
+								$order_shipment->remove_shipment( $id );
 							}
 
-							$shipment = wc_gzd_create_shipment(
-								$order_shipment,
-								array(
-									'items' => $shipment_items,
-									'props' => array(
-										'packaging_id' => $packaging->get_id(),
-										'status'       => $shipment_status,
-									),
-								)
-							);
-
-							if ( ! is_wp_error( $shipment ) ) {
-								$order_shipment->add_shipment( $shipment );
-
-								$shipments_created[ $shipment->get_id() ] = $shipment;
-							} else {
-								foreach ( $shipments_created as $id => $shipment_created ) {
-									$shipment_created->delete( true );
-									$order_shipment->remove_shipment( $id );
-								}
-
-								foreach ( $shipment->get_error_messages() as $code => $message ) {
-									$errors->add( $code, $message );
-								}
+							foreach ( $shipment->get_error_messages() as $code => $message ) {
+								$errors->add( $code, $message );
 							}
 						}
 					}
diff --git a/src/Order.php b/src/Order.php
index ff5803fd..4f957359 100644
--- a/src/Order.php
+++ b/src/Order.php
@@ -2,9 +2,9 @@
 
 namespace Vendidero\Germanized\Shipments;
 
-use DVDoug\BoxPacker\ItemList;
 use Exception;
 use Vendidero\Germanized\Shipments\Packing\Helper;
+use Vendidero\Germanized\Shipments\Packing\ItemList;
 use Vendidero\Germanized\Shipments\Packing\OrderItem;
 use Vendidero\Germanized\Shipments\ShippingMethod\MethodHelper;
 use Vendidero\Germanized\Shipments\ShippingMethod\ProviderMethod;
@@ -542,29 +542,38 @@ public function get_item_quantity_left_for_returning( $order_item_id, $args = ar
 	/**
 	 * @param false $legacy_group_by_product_group
 	 *
-	 * @return OrderItem[]
+	 * @return ItemList|OrderItem[]
 	 */
 	public function get_items_to_pack_left_for_shipping( $legacy_group_by_product_group = null ) {
 		$items              = $this->get_available_items_for_shipment();
-		$items_to_be_packed = array();
+		$items_to_be_packed = ! is_null( $legacy_group_by_product_group ) ? array() : new ItemList();
 
 		foreach ( $items as $order_item_id => $item ) {
 			if ( ! $order_item = $this->get_order()->get_item( $order_item_id ) ) {
 				continue;
 			}
 
-			$product_group = '';
+			$box_item = new Packing\OrderItem( $order_item );
 
-			if ( $product = $order_item->get_product() ) {
-				$product_group = Helper::get_product_packing_group( $product );
-			}
+			if ( ! is_null( $legacy_group_by_product_group ) ) {
+				$product_group = '';
 
-			if ( ! array_key_exists( $product_group, $items_to_be_packed ) ) {
-				$items_to_be_packed[ $product_group ] = new ItemList();
-			}
+				if ( $product = $order_item->get_product() ) {
+					$product_group = '';
 
-			$box_item = new Packing\OrderItem( $order_item );
-			$items_to_be_packed[ $product_group ]->insert( $box_item, $item['max_quantity'] );
+					if ( 'yes' === get_option( 'woocommerce_gzd_shipments_packing_group_by_shipping_class' ) ) {
+						$product_group = $product->get_shipping_class();
+					}
+				}
+
+				if ( ! array_key_exists( $product_group, $items_to_be_packed ) ) {
+					$items_to_be_packed[ $product_group ] = new ItemList();
+				}
+
+				$items_to_be_packed[ $product_group ]->insert( $box_item, $item['max_quantity'] );
+			} else {
+				$items_to_be_packed->insert( $box_item, $item['max_quantity'] );
+			}
 		}
 
 		return apply_filters( 'woocommerce_gzd_shipment_order_items_to_pack_left_for_shipping', $items_to_be_packed );
diff --git a/src/Packing/Helper.php b/src/Packing/Helper.php
index 1804843c..871960cb 100644
--- a/src/Packing/Helper.php
+++ b/src/Packing/Helper.php
@@ -76,22 +76,7 @@ public static function enable_auto_packing() {
 	}
 
 	/**
-	 * @param \WC_Product $product
-	 *
-	 * @return string
-	 */
-	public static function get_product_packing_group( $product ) {
-		$group = '';
-
-		if ( 'yes' === get_option( 'woocommerce_gzd_shipments_packing_group_by_shipping_class' ) ) {
-			$group = $product->get_shipping_class();
-		}
-
-		return apply_filters( 'woocommerce_gzd_product_packing_group', $group, $product );
-	}
-
-	/**
-	 * @param PackingItem[] $items
+	 * @param \Vendidero\Germanized\Shipments\Packing\ItemList $items
 	 * @param PackingBox[]|BoxList $boxes
 	 *
 	 * @return PackedBoxList
diff --git a/src/Packing/Item.php b/src/Packing/Item.php
index 00316c72..65688f67 100644
--- a/src/Packing/Item.php
+++ b/src/Packing/Item.php
@@ -53,6 +53,21 @@ public function canBePacked( $box, $already_packed_items, int $proposed_x, int $
 					$fits = false;
 				}
 			}
+
+			/**
+			 * In case grouping is activated make sure that a new item with a different shipping class
+			 * is not being packed within the same already existing package.
+			 */
+			if ( $fits && 'yes' === get_option( 'woocommerce_gzd_shipments_packing_group_by_shipping_class' ) ) {
+				$count     = $already_packed_items->count();
+				$last_item = $count > 0 ? $already_packed_items->getIterator()[ $count - 1 ]->getItem() : false;
+
+				if ( $last_item && ( $last_product = $last_item->get_product() ) ) {
+					if ( $last_product->get_shipping_class_id() !== $shipping_class ) {
+						$fits = false;
+					}
+				}
+			}
 		}
 
 		return apply_filters( 'woocommerce_gzd_shipments_item_fits_packaging', $fits, $this, $box->get_packaging(), $already_packed_items, $args );
diff --git a/src/Packing/ItemList.php b/src/Packing/ItemList.php
new file mode 100644
index 00000000..bd02f5b7
--- /dev/null
+++ b/src/Packing/ItemList.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Vendidero\Germanized\Shipments\Packing;
+
+defined( 'ABSPATH' ) || exit;
+
+/**
+ * An item to be packed.
+ */
+class ItemList extends \DVDoug\BoxPacker\ItemList {
+
+}
diff --git a/src/ShippingMethod/MethodHelper.php b/src/ShippingMethod/MethodHelper.php
index 896ecbe6..37b7550e 100644
--- a/src/ShippingMethod/MethodHelper.php
+++ b/src/ShippingMethod/MethodHelper.php
@@ -2,9 +2,9 @@
 
 namespace Vendidero\Germanized\Shipments\ShippingMethod;
 
-use DVDoug\BoxPacker\ItemList;
 use Vendidero\Germanized\Shipments\Package;
 use Vendidero\Germanized\Shipments\Packing\CartItem;
+use Vendidero\Germanized\Shipments\Packing\ItemList;
 use Vendidero\Germanized\Shipments\ShippingProvider\Helper;
 
 defined( 'ABSPATH' ) || exit;
@@ -62,26 +62,16 @@ public static function register_shipping_methods( $methods ) {
 	}
 
 	public static function register_cart_items_to_pack( $cart_contents ) {
-		if ( ! Package::is_packing_supported() ) {
+		if ( ! Package::is_packing_supported() || apply_filters( 'woocommerce_gzd_shipments_disable_cart_packing', false ) ) {
 			return $cart_contents;
 		}
 
 		foreach ( $cart_contents as $index => $content ) {
-			$items = array();
+			$items = new ItemList();
 
 			foreach ( $content['contents'] as $content_key => $data ) {
-				$cart_item     = new CartItem( $data, wc()->cart->display_prices_including_tax() );
-				$product_group = '';
-
-				if ( $product = $cart_item->get_product() ) {
-					$product_group = \Vendidero\Germanized\Shipments\Packing\Helper::get_product_packing_group( $product );
-				}
-
-				if ( ! array_key_exists( $product_group, $items ) ) {
-					$items[ $product_group ] = new ItemList();
-				}
-
-				$items[ $product_group ]->insert( $cart_item, $data['quantity'] );
+				$cart_item = new CartItem( $data, wc()->cart->display_prices_including_tax() );
+				$items->insert( $cart_item, $data['quantity'] );
 			}
 
 			$cart_contents[ $index ]['items_to_pack'] = $items;
diff --git a/src/ShippingMethod/ShippingMethod.php b/src/ShippingMethod/ShippingMethod.php
index d76919f8..a07dbf71 100644
--- a/src/ShippingMethod/ShippingMethod.php
+++ b/src/ShippingMethod/ShippingMethod.php
@@ -387,54 +387,81 @@ public function calculate_shipping( $package = array() ) {
 			$packaging_ids         = array();
 			$total_packed_item_map = array();
 			$total_packed_items    = 0;
+			$packed_boxes          = Helper::pack( $package['items_to_pack'], $boxes, 'cart' );
+
+			foreach ( $packed_boxes as $box ) {
+				$packaging        = $box->getBox();
+				$items            = $box->getItems();
+				$total_weight     = wc_get_weight( $items->getWeight(), strtolower( get_option( 'woocommerce_weight_unit' ) ), 'g' );
+				$volume           = wc_get_dimension( $items->getVolume(), strtolower( get_option( 'woocommerce_dimension_unit' ) ), 'mm' );
+				$item_count       = $items->count();
+				$total            = 0;
+				$subtotal         = 0;
+				$products         = array();
+				$shipping_classes = array();
+
+				foreach ( $items as $item ) {
+					$cart_item = $item->getItem();
+					$total    += $cart_item->getTotal();
+					$subtotal += $cart_item->getSubtotal();
+					$product   = $cart_item->get_product();
+
+					if ( $product && ! array_key_exists( $product->get_id(), $products ) ) {
+						$products[ $product->get_id() ] = $product;
+
+						if ( ! empty( $product->get_shipping_class_id() ) ) {
+							$shipping_classes[] = $product->get_shipping_class_id();
+						}
+					}
+				}
 
-			foreach ( $package['items_to_pack'] as $product_group => $items_to_pack ) {
-				$packed_boxes = Helper::pack( $items_to_pack, $boxes, 'cart' );
-
-				foreach ( $packed_boxes as $box ) {
-					$packaging        = $box->getBox();
-					$items            = $box->getItems();
-					$total_weight     = wc_get_weight( $items->getWeight(), strtolower( get_option( 'woocommerce_weight_unit' ) ), 'g' );
-					$volume           = wc_get_dimension( $items->getVolume(), strtolower( get_option( 'woocommerce_dimension_unit' ) ), 'mm' );
-					$item_count       = $items->count();
-					$total            = 0;
-					$subtotal         = 0;
-					$products         = array();
-					$shipping_classes = array();
+				$total            = wc_remove_number_precision( $total );
+				$subtotal         = wc_remove_number_precision( $subtotal );
+				$shipping_classes = array_unique( $shipping_classes );
+				$package_data     = array(
+					'total'            => $total,
+					'subtotal'         => $subtotal,
+					'weight'           => $total_weight,
+					'volume'           => $volume,
+					'item_count'       => $item_count,
+					'packaging_id'     => $packaging->get_id(),
+					'products'         => $products,
+					'shipping_classes' => $shipping_classes,
+				);
 
-					foreach ( $items as $item ) {
-						$cart_item = $item->getItem();
-						$total    += $cart_item->getTotal();
-						$subtotal += $cart_item->getSubtotal();
-						$product   = $cart_item->get_product();
+				$package_applied_rules = array();
+				$applicable_rule_costs = array();
 
-						if ( $product && ! array_key_exists( $product->get_id(), $products ) ) {
-							$products[ $product->get_id() ] = $product;
+				foreach ( array_reverse( $this->get_shipping_rules_by_packaging( $packaging->get_id() ) ) as $rule ) {
+					$rule         = $this->parse_rule( $rule );
+					$rule_applies = $this->rule_applies( $rule, $package_data );
 
-							if ( ! empty( $product->get_shipping_class_id() ) ) {
-								$shipping_classes[] = $product->get_shipping_class_id();
-							}
-						}
+					if ( $rule_applies ) {
+						$applicable_rule_costs[] = $rule['costs'];
+						$package_applied_rules[] = $rule['rule_id'];
 					}
 
-					$total            = wc_remove_number_precision( $total );
-					$subtotal         = wc_remove_number_precision( $subtotal );
-					$shipping_classes = array_unique( $shipping_classes );
-					$package_data     = array(
-						'total'            => $total,
-						'subtotal'         => $subtotal,
-						'weight'           => $total_weight,
-						'volume'           => $volume,
-						'item_count'       => $item_count,
-						'packaging_id'     => $packaging->get_id(),
-						'products'         => $products,
-						'shipping_classes' => $shipping_classes,
-					);
+					/**
+					 * In case a free shipping option is detected, stop + reset.
+					 */
+					if ( $rule_applies && 0.0 === $rule['costs'] ) {
+						$applicable_rule_costs = array(
+							$rule['costs'],
+						);
+
+						$package_applied_rules = array(
+							$rule['rule_id'],
+						);
 
-					$package_applied_rules = array();
-					$applicable_rule_costs = array();
+						break;
+					}
+				}
 
-					foreach ( array_reverse( $this->get_shipping_rules_by_packaging( $packaging->get_id() ) ) as $rule ) {
+				/**
+				 * In case no applicable rule has been found, parse fallback rules.
+				 */
+				if ( empty( $package_applied_rules ) ) {
+					foreach ( array_reverse( $this->get_fallback_shipping_rules() ) as $rule ) {
 						$rule         = $this->parse_rule( $rule );
 						$rule_applies = $this->rule_applies( $rule, $package_data );
 
@@ -458,114 +485,84 @@ public function calculate_shipping( $package = array() ) {
 							break;
 						}
 					}
+				}
 
-					/**
-					 * In case no applicable rule has been found, parse fallback rules.
-					 */
-					if ( empty( $package_applied_rules ) ) {
-						foreach ( array_reverse( $this->get_fallback_shipping_rules() ) as $rule ) {
-							$rule         = $this->parse_rule( $rule );
-							$rule_applies = $this->rule_applies( $rule, $package_data );
-
-							if ( $rule_applies ) {
-								$applicable_rule_costs[] = $rule['costs'];
-								$package_applied_rules[] = $rule['rule_id'];
-							}
-
-							/**
-							 * In case a free shipping option is detected, stop + reset.
-							 */
-							if ( $rule_applies && 0.0 === $rule['costs'] ) {
-								$applicable_rule_costs = array(
-									$rule['costs'],
-								);
+				if ( ! empty( $package_applied_rules ) ) {
+					$applicable_rules_total_cost = 0.0;
 
-								$package_applied_rules = array(
-									$rule['rule_id'],
-								);
+					if ( 'sum' === $multiple_rules_calculation_mode ) {
+						$applicable_rules_total_cost = array_sum( $applicable_rule_costs );
+					} elseif ( 'min' === $multiple_rules_calculation_mode ) {
+						$applicable_rules_total_cost = min( $applicable_rule_costs );
+					} elseif ( 'max' === $multiple_rules_calculation_mode ) {
+						$applicable_rules_total_cost = max( $applicable_rule_costs );
+					}
 
-								break;
-							}
+					if ( 'min' === $cost_calculation_mode ) {
+						if ( $applicable_rules_total_cost <= $total_cost || 0.0 === $total_cost ) {
+							$total_cost = $applicable_rules_total_cost;
 						}
+					} elseif ( 'max' === $cost_calculation_mode ) {
+						if ( $applicable_rules_total_cost >= $total_cost ) {
+							$total_cost = $applicable_rules_total_cost;
+						}
+					} else {
+						$total_cost += $applicable_rules_total_cost;
 					}
 
-					if ( ! empty( $package_applied_rules ) ) {
-						$applicable_rules_total_cost = 0.0;
+					/**
+					 * Build an item map which contains a map of the cart items
+					 * included within the package.
+					 */
+					$item_map = array();
+
+					foreach ( $items as $item ) {
+						$cart_item_wrapper = $item->getItem();
+						$product           = $cart_item_wrapper->get_product();
+						$product_key       = $product->get_parent_id() . '_' . $product->get_id();
 
-						if ( 'sum' === $multiple_rules_calculation_mode ) {
-							$applicable_rules_total_cost = array_sum( $applicable_rule_costs );
-						} elseif ( 'min' === $multiple_rules_calculation_mode ) {
-							$applicable_rules_total_cost = min( $applicable_rule_costs );
-						} elseif ( 'max' === $multiple_rules_calculation_mode ) {
-							$applicable_rules_total_cost = max( $applicable_rule_costs );
+						if ( array_key_exists( $product_key, $item_map ) ) {
+							$item_map[ $product_key ]++;
+						} else {
+							$item_map[ $product_key ] = 1;
 						}
 
-						if ( 'min' === $cost_calculation_mode ) {
-							if ( $applicable_rules_total_cost <= $total_cost || 0.0 === $total_cost ) {
-								$total_cost = $applicable_rules_total_cost;
-							}
-						} elseif ( 'max' === $cost_calculation_mode ) {
-							if ( $applicable_rules_total_cost >= $total_cost ) {
-								$total_cost = $applicable_rules_total_cost;
-							}
+						if ( array_key_exists( $product_key, $total_packed_item_map ) ) {
+							$total_packed_item_map[ $product_key ]++;
 						} else {
-							$total_cost += $applicable_rules_total_cost;
+							$total_packed_item_map[ $product_key ] = 1;
 						}
 
-						/**
-						 * Build an item map which contains a map of the cart items
-						 * included within the package.
-						 */
-						$item_map = array();
-
-						foreach ( $items as $item ) {
-							$cart_item_wrapper = $item->getItem();
-							$product           = $cart_item_wrapper->get_product();
-							$product_key       = $product->get_parent_id() . '_' . $product->get_id();
-
-							if ( array_key_exists( $product_key, $item_map ) ) {
-								$item_map[ $product_key ]++;
-							} else {
-								$item_map[ $product_key ] = 1;
-							}
-
-							if ( array_key_exists( $product_key, $total_packed_item_map ) ) {
-								$total_packed_item_map[ $product_key ]++;
-							} else {
-								$total_packed_item_map[ $product_key ] = 1;
-							}
-
-							$total_packed_items++;
-						}
+						$total_packed_items++;
+					}
 
-						$applied_rules[] = array(
-							'packaging_id' => $packaging->get_id(),
-							'rules'        => $package_applied_rules,
-							'items'        => $item_map,
-						);
+					$applied_rules[] = array(
+						'packaging_id' => $packaging->get_id(),
+						'rules'        => $package_applied_rules,
+						'items'        => $item_map,
+					);
 
-						$rule_ids      = array_unique( array_merge( $rule_ids, $package_applied_rules ) );
-						$packaging_ids = array_unique( array_merge( $packaging_ids, array( $packaging->get_id() ) ) );
-					}
+					$rule_ids      = array_unique( array_merge( $rule_ids, $package_applied_rules ) );
+					$packaging_ids = array_unique( array_merge( $packaging_ids, array( $packaging->get_id() ) ) );
 				}
 			}
+		}
 
-			if ( ! empty( $applied_rules ) ) {
-				$this->add_rate(
-					array(
-						'cost'      => $total_cost,
-						'label'     => $this->get_rate_label( $total_cost ),
-						'package'   => $package,
-						'meta_data' => array(
-							'_packed_items'    => $total_packed_items,
-							'_packed_item_map' => $total_packed_item_map,
-							'_packaging_ids'   => $packaging_ids,
-							'_rule_ids'        => $rule_ids,
-							'_packages'        => $applied_rules,
-						),
-					)
-				);
-			}
+		if ( ! empty( $applied_rules ) ) {
+			$this->add_rate(
+				array(
+					'cost'      => $total_cost,
+					'label'     => $this->get_rate_label( $total_cost ),
+					'package'   => $package,
+					'meta_data' => array(
+						'_packed_items'    => $total_packed_items,
+						'_packed_item_map' => $total_packed_item_map,
+						'_packaging_ids'   => $packaging_ids,
+						'_rule_ids'        => $rule_ids,
+						'_packages'        => $applied_rules,
+					),
+				)
+			);
 		}
 	}