I just did another probably dirty experiment, so don't blame me. I just want to report the results:
1. in Maverick I installed 'libc-bin' and 'libc6' (2.11.2-7) from Squeeze and
after reboot I got a corrupted filesystem (8 orphaned inodes) besides other complaints.
2. in Debian-Squeeze I installed 'libc-bin' and 'libc6' (2.11.1-0ubuntu7.6) from Lucid-updates and
after reboot I got a clean filesystem (no orphaned inodes) besides other complaints.
Disregarding the dirty way of using unmatched libc's and the resulting complaints of apt, ...
I conclude that the libc-packages of both, Ubuntu and Debian, themselfs are correct.
So the root of the evil has to be something else - I suppose upstart.
My personal opinion is that at very first this basic and critical bug must be fixed.
As log as this filesystem-corruption during shutdown persists, all the other related problems and bugs do just try to cure the symptoms and waste a lot of work?
Maybe I am wrong, but this bug though critical is not assigned to anybody yet. I wonder when somebody will feel responsible.