Comment 8 for bug 1274672

 I reported a similar bug as #1388511. Is it the same bug?

There's a workaround suggested at

http://askubuntu.com/questions/496401/how-to-upgrade-from-xserver-xorg-lts-saucy-to-xserver-xorg-lts-trusty

This involves removing the entire GUI, upgrading the distro, and reinstalling the entire GUI. That seems a bit much.