Comment 66 for bug 1236749

I experienced this problem on Ubuntu 14.10 with Gnome 3.12.2 when I upgraded from the Ubuntu packaged version of gnome to the gnome3-team version. Two other issues arose as well: gnome-terminal its lost profile settings and crashed when I tried to edit them, and the gdm login screen did not display any usernames. Maybe the dconf settings have become inconsistent across the two sources of gnome packages.

Comment #23 (resetting dconf) solved my problem.