Spacing is calculated incorrectly when the sticky element has side margins

[kevinthr]

Any time I put side margins on the sticky element, it gets placed wrong when it becomes sticky. If I give it a positive side margin, it gets stuck too far to the left; if I give it a negative side margin, it gets stuck too far to the right. Anyone else getting this behavior? I took a look at the library because I suspected that maybe it was using InnerWidth instead of OuterWidth to do calculations but no, it's using OuterWidth, so I'm not sure what's happening here.