Two panels can gets stuck into endless loop

[Ingo Ruhnke]

I am not fully sure if it is the gnome-panel or metacity who is causing the problem or something else and I haven't bothered to try to reproduce it in a clean environment. Anyway, way I produced the problem multiple times goes like this:

1) configure a dual monitor display with one workspace spanning the two screens (ATI proprietary drivers)
2) place a gnome panel at the bottom of each screen
3) fumble with the graphics drivers so that the computer will start in single screen mode (can happen by going back to the Open Source drivers or upgrading the proprietary ones)
4) the now single-screen desktop will not fully boot up, but instead get stuck on the gnome-panel, both panels seem to flicker at the bottom and gnome doesn't seem to be able to handle two panels at the bottom

Some further information:

Primary Screen (right): 1680x1050
Secondary Screen (left): 1280x1024

Ubuntu 11.04
gnome-panel 1:2.32.1-0ubuntu6.5
metacity 1:2.30.3-0ubuntu8