I think I may be getting listed, but for a very short period of time, and what I'm seeing are clients gathering their pings. Note the server is running on port 15000 here.
Master Server (Webserver list) Ping
Sep 19 07:36:16 10.25.10.254 id=firewall sn=0040100F1C5D time="2007-09-19 07:35:56" fw=74.129.231.5 pri=6 c=262144 m=98 msg="Connection Opened" n=8986 src=64.22.107.122:54133:WAN dst=74.129.231.5:13029:LAN proto=udp/13029
Heartbeat
Sep 19 07:40:23 10.25.10.254 id=firewall sn=0040100F1C5D time="2007-09-19 07:40:03" fw=74.129.231.5 pri=6 c=1024 m=537 msg="Connection Closed" n=3965 src=10.25.10.1:15000:LAN dst=64.22.107.125:27950:WAN proto=udp/27950 sent=249 rcvd=50
Client Ping
Sep 19 07:41:34 10.25.10.254 id=firewall sn=0040100F1C5D time="2007-09-19 07:41:14" fw=74.129.231.5 pri=6 c=262144 m=98 msg="Connection Opened" n=9101 src=217.224.77.55:27960:WAN dst=74.129.231.5:13029:LAN proto=udp/13029
The master server does not use the same ip to verify the server, and the router will not do any translation for a different ip, as this would make sense for security reasons. The router knows to translate incoming packets on the random port it chose to the real source port the server sent, but only for the original ip it sent it to. I think maybe it's being listed until the master server tries to verify it, from another ip address. I'll do some sniffing tonight, though, and see what I can find. I'm probably going to need to do it on the wan and lan sides simultaneously to get a clear picture.
EDIT:
I just verified that it is being listed, but since no one can get a reply from it, it doesn't show up in the listing, and doesn't show up in the master server web list either, since the webserver is using a different ip to ping the server. I used a local client, grabbed the master list several times, and checked the syslogs for my local ip. Sure enough there it was, trying to connect to the outside address, on the wrong port.
Sep 19 08:04:03 10.25.10.254 id=firewall sn=0040100F1C5D time="2007-09-19 08:03:44" fw=74.129.231.5 pri=6 c=262144 m=98 msg="Connection Opened" n=9743 src=10.25.10.62:27960:LAN dst=74.129.231.5:13081:LAN proto=udp/13081
So the server is definitely being listed, but the router isn't going to do any translation for any ip other than the ip it sent the heartbeat to. There's nothing wrong with the router, the way the heartbeat works is just incompatible with how this router works. I'm going to do some more testing with some other enterprise equipment at work and see if I get the same results. I should probably put the server in the DMZ anyway, at least to see if the problem persists, but unless I NAT it in the DMZ, I'll have to pay for another public address, and NAT'ing it in the DMZ surely will produce the same results.
EDIT2:
Tested on a Sonicwall 4060, same results.