I've KDE 4.14.3 on Funtoo Linux 64 bits. Sometimes kdm "crashes" switching user: for example: Reproducible: Sometimes Steps to Reproduce: 1.1) User 1 make the login 2) Using "switch useer", the 2nd user make a login. 3) the 2nd user close him session. 4) The kdm doesn't compare and i must manually shutdown and restart kdm from a tty (/etc/init.d/kdm restart). 2. 3. My system has a nvidia GTX660. The trouble is not related to "proprietary drivers" i think, since it the same situation also using "nouveau" drivers.
Closing as KDM is no longer maintained. Please switch to a different login manager, like SDDM or LightDM.