More information... The conditional formatting uses the formula
GetLayoutObjectAttribute( "panel4tab1" ; "isFrontTabPanel" ) = 1
It seems to redraw properly, always in Layout mode ( the conditional formatting changes as I change the tabs even in layout ). It seems to redraw properly, always when first switching to Browse mode, the default tab and all other tabs are all drawn correctly.
However, in two other situations it redraws improperly, or at least differently. The graphic in the above post shows that the redrawn formatting occurs correctly within the bounds of the tab panel, but not outside the panel. The split fill is the boundary of the tab panel. Also, if I move one of these completely outside of the tab panel it does not show the format change to either the font or the fill.
This seems like a Filemaker bug to me. Or is it my (mis)understanding of Filemaker intricacies?