remote GNOME session over ssh fails

[lloyd <subscr002@twilight-systems.com>]

I start a local X session and run a GNOME session on another machine:

  X &
  xterm -display :0 -e ssh -X -f remotehost gnome-session

For awhile this worked - now it's mysteriously not working.  I just get 
the blank X root window, and nothing else happens.

However, if I drop the -f parameter for ssh, it works:

  X &
  xterm -display :0 -e ssh -X remotehost gnome-session

...but I have an ugly xterm window on my display - disconcerting for 
non-techie users, who often close the window and thus end the GNOME 
session altogether.

any ideas what might be going on?