upgrade-problems with mount

[Stephen Rueger <stephen.rueger@hadiko.de>]

Hello!

The last time I made apt-get upgrade, it tried to update the package
mount to version 2.10s-2, but the following error occured:

dpkg: error processing /var/cache/apt/archive/mount_2.10s-2.deb 
	(--unpack):
unable to make backup link of '/bin/mount' before installing new
	version: [Operation not permitted]

(Things in [] are translated by me because I localized my system to
german.)

After that I tried to upgrade the package manually, but nothing
helped. I even tried to 'dpkg --purge mount' despite of the
dependancies, but it couldn't remove mount/umount, too.

After that I checked permissions, but they seem to be OK:
-rwsr-xr-x    1 root     root        25116 Nov 22 20:14 umount
-rwsr-xr-x    1 root     root        56284 Nov 22 20:14 mount

So what have I missed? Any hints, manpages or this only a bug and will
be fixed soon?

Thanks in advance!

Stephen Rueger