Gizmo, I'm running behind the same firewall my server is running behind. I loop out to my IP Gateway and right back in to the server. The IP Gateway is 11 IP addresses above the IP address the server is sitting under. Here are my results:

R 192.168.3.1
----------
R 192.168.3.1
----------
192.168.3.1

The IP address in this test is the LAN IP address for the firewall. The test PHP file is located at http://www.jaisp.com/ipheaders.php and this is what I typed in my web browser.

My Internal IP address is 192.168.3.15
My Server Internal IP address is 192.168.3.100