... it is not a bug.

A user without a password isn't allowed to handle with sshd. Therefore you have to run '/usr/sbin/sshstart' from Klaus Knopper. This script checks all necessary things and ask for a password for user "knoppix".

Greetings Werner * http://www.wp-schulz.de/knoppix/summary.html
Own Rescue-CD with Knoppix (Knoppix V6.4.4 remaster)