Comment 4 for bug 27338

This problem doesn't occur for me anymore since I've deleted the configuration folders in my home folder:
.gconf
.gconfd
.gnome
.gnome2
.gnome2_private
.gnome_private

Probably there is some incompatibility in the configuration between older and newer packages.

Can you try the following:
- Log out of Gnome
- move the folder mentioned above to another location
- Log in again

Does this also work for you?