i have the very same problem.
I use slackware 10.1 and upgraded to kde 3.4.1 by using the package on ftp.kde.org/stable/3.4.1/contrib/slackware/10.1. All worked fine.
I could have changed one time the settings of kdm from the kontrol center as a user and by typing the root passwd.
But now, every time i try that, it fails. i have some dcoperver process, and kdesud running ,but after some time kontrol center present me the default page that you have when you launch it; and not the page that is needed.
If i run manually the command kcmshell that is normally run (you could see it in the dialog asking your root passwd), everything works fine.
I think it is a bug and i may fil a bug report .