same problem here. Afters hours (3-4H, random) , session becomes slow, clic very long to respond. No network problem, no load or CPU high on server, everything is normal on server.
I was unable to reproduce at any time. and i wad unable to guess what KDE4 app is problem. Application that are used : Dolphin, Open Office Calc, sometimes Firefox
Closing session et restart it is OK.
I can make some tests or look for logs if you want..