When running grml-live with a local mirror (and no public mirror) it works fine 
but when re-running grml-live with the -u option the default mirror 
configuration in /etc/apt/sources.list.d/debian.list is being used.

Solution: remove /etc/apt/sources.list.d/debian.list and rewrite the list for 
FAI's softupdate, then restore the default again through SCRIPTS/....