Locking up when logging out.

[Christian]

Hi,

I am running Ubuntu 13.10 x64 on a Thinkpad laptop. Everything works 
except for one thing: Often when I log out of a account I end up with a 
black screen with a blinking cursor "-" on the top left of the screen. 
The only way out of it is opening another console and reboot from there. 
I have tried to kill the locked up session but do not know how to get 
back to a login prompt. This doesn't happen all the time but it is 
probably around half of the times I log out. Otherwise my install is 
pretty standard running Unity as desktop and LightDM as display manager. 
There's no such problems when I reboot.

Any idea what may be causing this?

-- 
//Christian