X over ssh

[Michael Naumann <michael.n@strux.net>]

I'm a bit clueless now.
Hopefully anybody can help me out here.
I have two machines m1 and m2 (both woody) connected.
I can ssh -X successfully from  m1 to m2 and vice versa.
Now my problem
on m1
  ls ~/.ssh
    -> authorized_keys  id_rsa  id_rsa.pub  known_hosts
  ssh -X m2 xlogo
    -> displays the logo on m1
  ssh -X m2 'echo $DISPLAY'
    -> localhost:14.0
on m2
  ls ~/.ssh
    -> authorized_keys  id_rsa  id_rsa.pub  known_hosts
  ssh -X m1 xlogo
    -> Error: Can't open display: 
  ssh -X m1 'echo $DISPLAY'
    -> <EMPTY> (And this seems to be my problem)

What I already checked:
  on both machines
    sshd (version OpenSSH_3.4p1 Debian 1:3.4p1-1) is started as
      /usr/bin/sshd (whithout any arguments)
    X11 ist started as
      /usr/X11R6/bin/X -dpi 100 -nolisten tcp vt7 -auth /var/lib/kdm/authfiles/xxxx
    grep -s DISPLAY ~/.* ~/* ~/.ssh/*
      shows no results
    cat /etc/ssh/ssh_config 
      gives no lines that are not commented

So I do not see any difference and yet, X over ssh only works in one direction.

Any pointer gladly apriciated,

Michael