Comment 0 for bug 1455278

I'm using Kubuntu 15.04 with latest plasma-desktop 4:5.2.2-0ubuntu4 version, with sddm.
When I look at my desktop background, I get the attached screenshot. This is the first time this happens, last logins were ok.
The content of the background changes, depending on which window has been highlighted before. When I have firefox and hexchat open, and switch from hexchat to firefox, the desktop content changes to hexchat.