ssh X forwarding not working through NAT

[Doug Poland]

Hello,

Occasionally I need to tunnel X via ssh to remote hosts.  I just built a 5.2.1-R system
and noticed that X does not forward from this machine to the outside via our NAT'ing
firewall.

If I connect to a host on the same network with:
  ssh -X me at insidehost

and type:
  echo $DISPLAY
localhost:11.0

On a machine outside the NAT/firewall that is behind it's own NAT/firewall I get...
DISPLAY: Undefined variable.

Now I know this worked on 4.9-STABLE boxes before.  Is there something new in 5.x that
prohibits X11 forwarding?   I have no ~/.ssh/config file and my /etc/ssh/ssh_config is
a stock file, untouched by human hands.

All clues and gentle prods are welcome.

-- 
Regards,
Doug