After a bit more investigation, it seems that it's the whole titlebar that does not refresh, not only the buttons. So if I switch tabs in FireFox the title does not update.
Also at random the titlebar of a window might suddenly start working (refreshing). I'm not sure what triggers it, but when a titlebar starts working it continues to do so until the window is closed.
I also tried Unity 2D and it does not have this bug.
After a bit more investigation, it seems that it's the whole titlebar that does not refresh, not only the buttons. So if I switch tabs in FireFox the title does not update.
Also at random the titlebar of a window might suddenly start working (refreshing). I'm not sure what triggers it, but when a titlebar starts working it continues to do so until the window is closed.
I also tried Unity 2D and it does not have this bug.