NACK for the workaround, as there might be side-effects not worth its effort. 
The reason for the behaviour is that the loopback device /dev/loop0 is pointing 
to /grml*.squashfs instead of /live/image/live/grml*.squashfs in /proc/mounts.
/etc/mtab is fine - so even mount -n ... might not help.

If anyone is interested in fixing the bug feel free to send a patch/bugreport 
to live-initramfs/initramfs-tools and reopen this bugreport. Closing this 
bugreport with "won't fix" in the meanwhile.

regards,
-mika-