I accidentally closed a panel properties menu (I think
the panel properties, but might have been global panel
properties) and the whole panel instantly disappeared.
No panel process existed, but when I tried to bring up
another panel from a terminal session, I was told that
another panel was running.
After logging out of my session, gnome-session would not
start anything until I deleted .gnome/session; then I got
a chance to start over with a fresh session...
Might be fixed by new panel/session code?
This seems to be fixed now. (This was probably caused a
bug in GDK where sometimes the WM_DELETE property
would not be set on things started before the WM)