Some of these problems are really nasty. A quick check in the internet revealed that there are quite a few of this same problem reported. Some says it's due to the CDROM, but there is probably no single cause for such misbehavior, so I guess 'udevadm' is probably the best choice for checking root cause. Upgrade the udev version might be an easier thing to try.

Fortunately I have never have to deal with this problem. However, I do encounter some other nasty problems though. They are widely reported problems, so have nothing to do with knoppix per se.