untrusted versions of the following packages will be installed

[Martin Konrad]

Hallo,
I ran into the following problem by just trying to upgrade one of the FAI 
packages on my FAI server from 3.4.4 to 3.4.5:

----------
# aptitude upgrade fai-doc
The following packages will be upgraded: 
  fai-doc 
1 packages upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
Need to get 639 kB of archives. After unpacking 12.3 kB will be freed.
Do you want to continue? [Y/n/?] 
WARNING: untrusted versions of the following packages will be installed!

Untrusted packages could compromise your system's security.
You should only proceed with the installation if you are certain that
this is what you want to do.

  fai-doc 

Do you want to ignore this warning and proceed anyway?
To continue, enter "Yes"; to abort, enter "No":
----------

What's the cause for that? I have the key in my apt keyring:

----------
# apt-key list
/etc/apt/trusted.gpg
[...]
pub   1024D/AB9B66FD 2000-08-18
uid                  Thomas Lange <lange at debian.org>
uid                  Thomas Lange <lange at informatik.uni-koeln.de>
sub   1024g/F526E7DB 2000-08-18
----------

The same problem arises during installation of a client machine. This error is 
fatal for me because I'm using FAI_ALLOW_UNSIGNED=0.

Cheers

Martin

-- 
Dipl. Phys. Martin Konrad
Technische Universität Darmstadt
Institut für Kernphysik
Schlossgartenstr. 9
64289 Darmstadt
Tel: +49-6151-16-5121
Fax: +49-6151-16-4321