New Post: Border thickness consistency between LayoutAnchorablePaneGroup and LayoutDocumentPaneGroup

Not really helping you but I noticed this problem too (mesured 2px difference) and it bother me but I didn't managed to fix it actually.
I noticed the margin difference between the tab panel in DocumentPaneControlStyle (2,2,2,0) and AnchorablePaneControlStyle (2,0,2,2).

I'll follow this thread, and hope someone has the solution !