Trying to open, and keep open, port 23456 in the ICF.

Strange happenings. I open UDP port 23456 in the ICF of
XP Home SP1 to connect to multiplayer sessions of Flight
Sim 2004. Once this port is opened and saved, I try to
connect to multiplayer session using that port. No
surprise...it doesn't connect. (Given the amount of
trouble I've had since I got a non-UPnP DSL Router from my
ISP, this is not unexpected.) I exit out of FS2004 and
check the ICF to validate that 23456 is open, only to find
out that my opening of 23456 has vaporized. Nothing
there.

I add it again and save it again and start up FS2004 again
and again no connection. Verify again that the port is
still open and again...it...is...gone. Just for laughs I
did it one more time to be sure. I'm sure.

I've found that Port 23456 is commonly used by the
worm "EvilFTP". I have Norton running the background but
not the internet firewall thingy that Norton put out.
Given that the Port 23456 has been identified as a risk,
would Norton or XP automatically remove it from the list
of open ports in the ICF if it was attempted to be used?

Thoughts?