Yeah, this clearly is an issue of the squeeze->wheezy upgrade.

Everyone stumbling upon this issue should use a base.tgz based on >=wheezy (see
http://grml.org/grml-live/#create-a-base-tgz) when using >=Debian/wheezy instead
of using a squeeze chroot.

I couldn't find a way how to get rid of is this issue and don't want to waste
any more time with it, so marking this one as won't fix.