Description:
some times gnome 3.6.2 lock screen goes crazy, so it can't unlock user desktop, and sometimes it's stop handling escape hotkey to show login unlock prompt 

Additional info:
It's very difficult to reproduce a problem with above states specially, because it's appears randomly after sleep
But I found a synthetic keyboard and mouse cobinantion I can make lock screen unworkable

Steps to reproduce:
1. Lock the screen
2. Left mousedown on screen bottom and move on near the screen top to unlock way, but do not release mouse
3. Press ESC key simulately and wait for a lock screen appears. _continue hold the mouse at this step_
4. Contimue to move mouse on screen top
5. You'll get gray screen without any prompt and key handling ;)

Discussion:
https://bugs.archlinux.org/task/32595