apt changes mount status of /usr ?!?!!

[Alexander List <alexlist@sbox.tu-graz.ac.at>]

Hi,

I've got slink running, just tried an upgrade with apt and encountered the
following weird behaviour:

linux:/home/alex# mount
/dev/hda2 on / type ext2 (rw,errors=remount-ro)
proc on /proc type proc (rw)
/dev/hda5 on /home type ext2 (rw,errors=remount-ro)
/dev/hda6 on /usr type ext2 (rw,errors=remount-ro)
/dev/hda7 on /var type ext2 (rw,errors=remount-ro)

linux:/home/alex# apt-get upgrade             
Reading Package Lists... Done
Building Dependency Tree... Done
The following packages have been kept back
  emacs20 emacs20-el 
0 packages upgraded, 0 newly installed, 0 to remove and 2 not upgraded.
1 packages not fully installed or removed.
Need to get 0B of archives. After unpacking 0B will be used.
Do you want to continue? [Y/n] y
Setting up cbb (0.81-0) ...
Update-menus: waiting for dpkg to finish(forking to background)
Update-menus: (checking /var/lib/dpkg/lock)
cannot open dhelp file '/usr/share/doc/cbb/html/.dhelp': at
/usr/sbin/install-docs line 534.
dpkg: error processing cbb (--configure):

 subprocess post-installation script returned error exit status 2
Errors were encountered while processing:
 cbb
E: Sub-process returned an error code (1)
linux:/home/alex# mount
/dev/hda2 on / type ext2 (rw,errors=remount-ro)
proc on /proc type proc (rw)
/dev/hda5 on /home type ext2 (rw,errors=remount-ro)
/dev/hda6 on /usr type ext2 (ro,errors=remount-ro)
/dev/hda7 on /var type ext2 (rw,errors=remount-ro)


Obviously, apt seems to fiddle around with mount during the upgrade
procedure, /usr is mounted ro after the upgrade!!!

On another system using slink, I noticed that apt doesn't work correctly
if there's no separate mount point for /usr, eg when you put everything in
one big partition. Did anyone else encounter similar problems?

I'd just like to ask, before I report this as a bug...

Alex