Whilst I know this solution will work for Gnome, I'm going to *guess* that it'll work for KDE, and some preliminary googling indicates that it should. The very worst that could happen is that you'll have to reverse the simple step.
Login to a console as the affected user and:
Code:
user$ mv .kde .kdebak
Now, login to kde as the affected user, and kde will recreate the user's config. Any of the previous customizations will be in .kdebak, so you should be able to restore them one-by-one.
hth