i'm using KDE 4.13.2 in kubuntu...

but sorry, in the end installing libdbusmenu-qt-dev didn't work for me. the problem still appears ramdomly...

i also tried installing kdm (i was using lightdm) but the problem keeps appearing...

it's very anoying, i also noted that some programas don't start either, like kmix and hplip, and they have to be started manually...

i hope we find a solution soon

Ok, i think i solved this problem... i followed this thread: https://bbs.archlinux.org/viewtopic.php?id=106612

and particularly the one post that says:

"After reading this thread, I deleted ksmserverrc with no luck. then 'killall ksmserver' activated the reboot.
I was using phonon-xine, so after the reboot I switched to phonon-gstreamer and everything seems to work fine now "

in my case, the system setting said VLC for the backend... i switched to gstreamer and i think it solved my problems...

hope it helps...