Hi Mark,
You are correct, WPF seems to be telling the button it has mouse over when it is tapped. But it never tells the button on tap release that the mouse is no longer over it. Then if you tap another control, WPF finally tells the original button that it no longer has mouse over and it updates its state.
I am seeing the same thing with a regular WPF ToolBar too (such as in our SDI Editor sample), even without our native themes active. We did some searching on the web and found a couple instances of this being reported in general. But there don't appear to be any good solutions. Unfortunately I'm not sure there's anything we can really do on our end about this, since it's happening with the native controls as well. Perhaps if something could be simulated to cause the IsMouseOver state to change, that would work around the problem?