Comment 212 for bug 438868

Still happens in Ubuntu 12.04 (and 11.04) for me, triggered whenever I window-shade for example Thunderbird or Firefox. Minimizing and restoring the window helps. According to other messages here, screensaver and thus standby also always triggers it. I also confirm that focusing another window for a moment helps.

The symptom of the bug is that in Firefox URL autocompletion, the list of suggestions immediately vanishes when it is about to show up and that all sorts of menus vanish at the moment when I try to move the mouse over them. For example I click on FILE, a menu shows up, I move the mouse to the menu, it vanishes. VERY frustrating. Sometimes using hotkeys helps, but by far not everything works without mouse. According to this bug discussion, the problem might be the Z window stacking of compiz messing up and getting fixed by being reset using the minimize-restore or focus-something-else workarounds.

This might also be related to: https://bugs.launchpad.net/ubuntu/+source/unity/+bug/968332