this is normal for strange creepy whatever reasons. some stuff in the network lib I use. I don't really know what's going on there to be honest but that's how it is.
your server is normally reachable under the port that is saved in the serverlist (that's the port that your server used to subscribe to the list), even if you specified (and forwarded) another port. it should also be reachable with the port you specified.
also I noted that this happens only when you host your server from your home PC and not when you host it on a real (v)Server (specified and listed ports are always the same in the latter case). so NAT routing stuff could be the answer indeed. I'm actually pretty sure that this must be the reason when thinking about it...