I have gnome-session (2.14.1-0ubuntu11) and xserver-xorg-input-evdev (1.1.2-0ubuntu3) installed and the bug is fixed.
I'm not sure if it works in every setup though, g-s-d isn't really handling multiple mouse buttons well. -- gconf2 2.12.1 not working (dapper) https://launchpad.net/bugs/26523 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
