[stupid-boy]

ok, it is clear you didn't looked at code. will explain in short.
this function changes alpha and sets this button focused in order to use its focused image. that SetFocus invalidates its region. after Process it restores button to unfocused, again invalidating it, but this time without result. trick used here is focused image + some alpha to made that glory.

..... and debugging this you will end with 2 focused controls at the same time, don't ask me how stupid i was looking at debugger at this moment ....