I have a dirty solution. Add:
in the beginning of /etc/init.d/kdm (e.g. just above "set -e"), then the touchpad is recognized as such in kde. This should be a "solution" for kubuntu.
If you use ubuntu, you will probably use gdm as window manager. I suppose you can do the same with gdm as I did with kdm.
I wonder if this bug is just a question of when the psmouse driver is started? I.e. if it started too early, the touchpad is recognized a mouse, only.