5.1p1 and X11 forwarding failing

[Jeff Blaine]

I'm really scratching my head on this one.  The server
is running OpenSSH 5.1p1 on Solaris 9.  The authentication
is via PAM if that matters.

# grep X11 sshd_config | sed '/^#/D'
X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost yes
#

Now I attach to my 'master' sshd and follow all children
to look for any evidence of "DISPLAY":

# truss -f -a -e -p 14923 2>&1 | grep DISPLAY

I then fire up ssh -X from a client machine, login, and
truss reports nothing.

If I perform the EXACT same test against stock Solaris 9
sshd (also authenticating against PAM), DISPLAY shows up
(in truss and in the shell) and X11 forwarding works fine.

Any ideas?