Filesystem permissions messed (0777) after update

Since December 2010 I had the problem 3 times on my Ubuntu 10.04 LTS (amd64). I agree to install updates, proposed by the update manager. After the installation is finished, I am asked to reboot the machine. Right after the restart of the machine all the file perms are set to 0777, recursively! So this of course affects /usr and /lib, meaning no setuid flag is set anymore and no 'sudo' is possible anymore. Booting from a rescue CD and adjusting the perms will be overwritten during the next startup. My machine runs the Linux system on a separate SATA disk on ext3. The data is on a 2 disk software RAID (mirror 'md0' using 'mdadm') mounted during startup. I saw several people having the same problem since about one year, but obviously it applies only to a special setup. On my second box, which is almost the same (almost a clone of the first), the problem never occurred. But I can reproduce the problem easily: simply apply the latest update (say the one of 2011-01-10) and restart and...'kawumm'.

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: update-notifier 0.99.3
ProcVersionSignature: Ubuntu 2.6.32-27.49-generic 2.6.32.26+drm33.12
Uname: Linux 2.6.32-27-generic x86_64
NonfreeKernelModules: nvidia
Architecture: amd64
Date: Tue Jan 11 21:47:46 2011
ExecutablePath: /usr/bin/update-notifier
InstallationMedia: Ubuntu 10.04.1 LTS "Lucid Lynx" - Release amd64 (20100816.1)
ProcEnviron:
 LANGUAGE=en_US.UTF-8
 LC_TIME=en_US.UTF-8
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: update-notifier
XsessionErrors: (polkit-gnome-authentication-agent-1:2152): GLib-CRITICAL **: g_once_init_leave: assertion `initialization_value != 0' failed