Whenever I try to logout by clicking on a logout option, the screen goes gray with the mouse cursor present and movable.  The only way I can recover is to power off or alt-f6 to a console and use init 0 or init 6. I am using 4.11.2 with Kubuntu 12.04 LTS.

Reproducible: Always

Steps to Reproduce:
1. Right click on the desktop, select 'Leave'
2. Select 'logout'
3. Also happens if 'logout' is selected via the launcher
Actual Results:  
The screen goes gray with only the mouse pointer active.  The graphical interface is frozen at that point.  Using Ctrl-Alt-F2, F3 and so on allows operation through the console. At this point, after logging in on the console, commands such as 'init 0' or 'init 6' can be entered to restart the system.

Expected Results:  
KDE should have logged off the current user and prompted for new user.

I am connected to the Kubuntu backports repository and keep up with KDE releases that way.  
Linux trekker-HP-G62 3.2.0-55-generic #85-Ubuntu SMP Wed Oct 2 12:29:27 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

Distributor ID: Ubuntu
Description:    Ubuntu 12.04.3 LTS
Release:        12.04
Codename:       precise