Bug#491879: kwin does not launch automatically at starting an session
So I came back home, downgraded my desktop and... it didnt work O.o
Still had this problem. But i remembered that I played with some
session settings at work. Setting "Restore manually saved session" and
then "Save session" in menu did the trick. Did some reboots and
logoffs, returned to "Restore previous session" and everything worked
just fine. Then upgraded, first reboot it worked. Sadly just first. I
loged off and kwin didnt start again.