Hi,
This is a feature, not a bug.
See

http://www.knoppix.net/forum/viewtopic.php?t=17347

and

http://www.knoppix.net/forum/viewtopic.php?t=18459

Logging out of KDE as a normal user, and then logging in as root from a console, and issuing startx command from there will also enable a graphical interface as user root iirc.
Regards,
Mark