Dedicated server - clearly I am the stupid

I cannot for the life of me figure out why the dedicated server for ARK insists on listening on one port (7778), but shows up in the server browser as on a different port (7777). 27015 listens correctly, and it's fine.

Doesn't matter how long I wait, the server simply does not ever listen on the same port it announces itself on to the server browser. I've tried several different setups (two different Ubuntu 14.04 LTS 64-bit systems, and Windows 8.1 64-bit) and none of them listen on the same port they announce.

Clearly other people have this working, but I cannot see what the hell I'm doing wrong. I've never had so much trouble running a dedicated server.

Netstat output below:

udp        0      0 0.0.0.0:27015           0.0.0.0:*                           4771/ShooterGameSer
udp        0      0 0.0.0.0:37241           0.0.0.0:*                           4771/ShooterGameSer
udp        0      0 0.0.0.0:7778            0.0.0.0:*                           4771/ShooterGameSer

Command line given to start it is basic, and I've checked the various ini files for ports (there are no references to ports):

./ShooterGameServer TheIsland?listen -nosteamclient -server -log -game

Oh yes, I've done all the open file handles hacking:

$ ulimit -n
1000000

And pam_limits.so is in the right place in PAM, and limits.conf is set to allow the raised limit.

Nope, does not want to listen on the correct port :(