dist-upgrade wants to remove gdm

[Hugo Vanwoerkom <hvw59601@care2.com>]

Hi,

I run Sid. I installed gdm instead of gdm3. But now dist-upgrade wants 
to remove gdm and gdm-themes.

hugo@HDBB:~$ apt-cache policy gdm
gdm:
  Installed: 2.20.7-4lenny1
  Candidate: 2.20.7-4lenny1
  Package pin: 2.20.7-4lenny1
  Version table:
 *** 2.20.7-4lenny1 1001
        500 http://ftp.de.debian.org/debian/ lenny/main amd64 Packages
        100 /var/lib/dpkg/status

How do I find out why?

Hugo