HDPublicKey child derivation broken

[raucao]

When initializing a new HD public key prototype from a string, I get an exception when using deriveChild() on it:

> var hdpub = new bitcore.HDPublicKey('ypub6XdVpDbc22LAzsE5kRjZUbSfTi5GQRsVPFM35riMikM47bZSPUAiNcZ1JxzXmon45saE4X5LhcRiysKBz3hVt2oqwhr7hoUVomTcVjeM8kG')
undefined
> hdpub.deriveChild(0)
AssertionError [ERR_ASSERTION]: version argument is not a buffer, it's undefined
    at checkBuffer (/home/basti/src/solarisbank/crypto-custody/api/node_modules/bitcore-lib/lib/hdpublickey.js:371:5)
    at Function.HDPublicKey._validateBufferArguments (/home/basti/src/solarisbank/crypto-custody/api/node_modules/bitcore-lib/lib/hdpublickey.js:377:3)
    at HDPublicKey._buildFromBuffers (/home/basti/src/solarisbank/crypto-custody/api/node_modules/bitcore-lib/lib/hdpublickey.js:328:15)
    at HDPublicKey._buildFromObject (/home/basti/src/solarisbank/crypto-custody/api/node_modules/bitcore-lib/lib/hdpublickey.js:289:15)
    at new HDPublicKey (/home/basti/src/solarisbank/crypto-custody/api/node_modules/bitcore-lib/lib/hdpublickey.js:58:23)
    at HDPublicKey._deriveWithNumber (/home/basti/src/solarisbank/crypto-custody/api/node_modules/bitcore-lib/lib/hdpublickey.js:173:17)
    at HDPublicKey.deriveChild (/home/basti/src/solarisbank/crypto-custody/api/node_modules/bitcore-lib/lib/hdpublickey.js:144:17)

The initialization doesn't seem to set all the extra properties on the object, like e.g. network, for some reason.