About once every other day my Ubuntu 11.10 Desktop screen gets in a state where the Application Switcher overlay won't go away. This is the overlay in the middle of screen that appears when you press ALT+Tab. The mouse remains responsive but nothing I do will make the overlay go away. And then after pressing more keys, a second overlay (with a different order of app icons) appears over the first, and now neither will go away.
I'd like to know if I can fix this. But if I can't, then I'd like to know how I can restart the desktop window manager but keep my Tmux sessions intact.