You should have a .xsession-errors file in your home directory. You might give that a look if you've not already done so. I've found it to be pretty helpful for these kinds of problems. Also, are you getting any type of KDE crash window? If so, click on the "Backtrace" tab. You should see a trace of the crash which may give you some indication of the modules involved. You could also save that output and then post it in a reply in this thread to see if anyone recognizes more about the problem. I've dealt with a couple of instances of the kind of problem you're describing. KDE is VERY dependent on the release of qt you're running, so, if you can get to a point you can query the qt level, you might take a look at whether there are any bug reports on http://bugs.kde.org
that can give you some advice on either upgrading or downgrading your qt level as a way of dealing with this. Just a few ideas. Hope this helps.