Sometimes when the menues disappears in Gnome. For example the bottom one disappears and there is a "hole" below the current window. When I move the mouse over the top menu the whole screen seems to update and the menu goes back, but it disappears again when I move the mouse off the top menu (this time without the whole screen updating).

The same thing can happen but reverse (that is that the top menu disappears and I can get it back by hovering over the bottom menu). I can temporarily fix this by right-clicking on the not-disappeared menu and move down/up the popup-menu until I reach the current window/background (this seems to "fool" the bug some way) and then with a simple click the popup menu is gone but both menues are back to normal (until I hover one menu again, then the other one disappears).

I tried to google for this but the only thing I found was how to fix some KDE menu-problem in Mandrake.

I am using a GeForce FX5500 if that would have something to do with it. Worth a mention.