Comment 30 for bug 346655

OK i've found on a french kubuntu forum the way to bypass the bug !
I don't know if it's KDE bug-related or Kubuntu, but to me i's a bug.

Here is the way :
Go to System Setings > Advanced tab > choose Session Manager, Users tab.
User's image source : check the box "User, System".

Facts that generate the bug :
I think the 1st time you change and save the settings inside the Session manager and don't pay attention to the user's image source, you can't change your image anymore (i guess default setting is on "system").