Comment 8 for bug 203527

I think the medium classification for this is too low. This can really impact your system. If you don't have a terminal window open and no shortcut to one on the desktop you are effectively locked up. Alt+F2 fails me in this situation, too.

I also had a complete system hang sometime after leaving gnome-panel in this state without killall -1 gnome-panel, which corrects the problem.