I am not using any nvidia hardware and I have this exact same issue. I believe the bug is within lightdm.
** Changed in: linux (Ubuntu) Status: Incomplete => Confirmed -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xserver-xorg-video-nouveau in Ubuntu. https://bugs.launchpad.net/bugs/1247189 Title: [13.10] Ubuntu freezes completely when switching user To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1247189/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp