Exactly the same problem for me since 12.04 (whereas that point was ok on 11.10).
I don't know what additionnal informations coud be usefull ...
I'm running Unity 3D on a laptop, up-to-date 12.04 installation upgraded from 11.10.
I'm encountering this problem right now with the "static application switcher" alt-tab behavior, but the problem was the same with the default unity alt-tab mechanism.
Exactly the same problem for me since 12.04 (whereas that point was ok on 11.10).
I don't know what additionnal informations coud be usefull ...
I'm running Unity 3D on a laptop, up-to-date 12.04 installation upgraded from 11.10.
I'm encountering this problem right now with the "static application switcher" alt-tab behavior, but the problem was the same with the default unity alt-tab mechanism.