Ubuntu 12.04. The first time I log into Gnome Classic I get a duplicate of every menu, panel indicator and taskbar entry. If I log out and back in again I now have three copies. Log out and log in, four copies and so forth.

What would cause this? I can't see any obvious duplicates in the process list:

$ ps -A | grep 'gno\|org\|nau'
27439 tty7     00:00:18 Xorg
27610 ?        00:00:00 gnome-keyring-d
27621 ?        00:00:00 gnome-session
27674 ?        00:00:00 gnome-settings-
27709 ?        00:00:07 gnome-panel
27720 ?        00:00:00 gnome-fallback-
27726 ?        00:00:04 nautilus
27736 ?        00:00:00 polkit-gnome-au
28281 ?        00:00:00 gnome-screensav
29016 ?        00:00:00 gnome-terminal
29021 ?        00:00:00 gnome-pty-helpe

If it helps, I was recently trying the Nouveau drivers but have now reverted to NVIDIA. Configuration is Separate X Window, Xinerama enabled. Unity is fine, so the problem is limited to the Classic desktop.

I haven't had any luck googling these particular symptoms so any tips would be really appreciated. Thanks!