The change_owner function did more than query /etc/passwd. It also prepended $DPKG_ROOT to the path it acted upon. So if you didn't do more than what you described above, then the result is incomplete.
Big oops! I guess every (old) call to change_owner is wrong now.
I'll send you a new tested patch once your upload reaches my mirror.
Ok, in case it helps, this is what I uploaded: https://people.debian.org/~sanvila/base-files/ Feel free to reopen the bug. Thanks.
