[SOLVED] Strange KDE behaviour with 2 logged in users

Background: Those two users (my wife and me) have the same primary group as we share pictures and some documents. I think that this might be related. But I might be wrong.
Symptoms: All windows from saved session are unavailable. They don't open on a click in a tray and they don't show themselves in Alt-Tab either. As saved session is very useful in my workflow this situation is extremely annoying.
Tests: I tried with fresh install of mga4 b2 and symptoms are the same.
Any idea how to deal with this situation?
Symptoms: All windows from saved session are unavailable. They don't open on a click in a tray and they don't show themselves in Alt-Tab either. As saved session is very useful in my workflow this situation is extremely annoying.
Tests: I tried with fresh install of mga4 b2 and symptoms are the same.
Any idea how to deal with this situation?