I figured out what's going on, but I still have a question...
What's going on: Switching tabs can still be done, but one has to be careful to avoid clicking on the 'customized' area of the tab. In other words, if you click on the Button embedded in the tab, the Button absorbs the click and the tab sees nothing.
Where this becomes a problem is when I embed a DrawingArea on which I draw a custom tab shape. The DrawingArea absorbs the click and so, still, the tabs doesn't see it.
So, now I'm looking for a way to pass along the click from the DrawingArea to the tab. I guess this could be done by having the DrawingArea react to the signal and pass it along... Hmmm... Not sure.
I just assumed the tab would get the click signal no matter what was stuffed into it.
Anyway, I'm still digging around for an answer, but if you know of a way, I'd appreciate if you passed it along, Mike.