Problem solved buddy. I was right. Phex was confused and didn't know its IP because it hadn't connected to anyone to get a response which it gets it's IP from. (Same process as those dynamic DNS clients discovering an IP even though they're behind NAT).

The solution was sneaky. First allow Phex to connect to the open GNUTELLA network. That'll get Phex to learn it's IP. Then disconnect, change to the private network and bingo. Everything is fine.

Gregor you might want to save that one for some documentation or maybe put in a field to enter a real IP address. This was what I assumed (wrongly) that Export Host IP As: would do.