FWIW, I'm also on 14.04 LTS and the workaround from comment #127 did not work for me. (nor any of the other lightdm work-arounds.)
The "fix" to switch to GDM worked for me
--BUT--
If you set your screen to shut off and require a password (in the Brightness & Lock settings), you'll get this bug still, even with GDM as your login manager.
FWIW, I'm also on 14.04 LTS and the workaround from comment #127 did not work for me. (nor any of the other lightdm work-arounds.)
The "fix" to switch to GDM worked for me
--BUT--
If you set your screen to shut off and require a password (in the Brightness & Lock settings), you'll get this bug still, even with GDM as your login manager.