[Freeswitch-users] NAT issue with registration responses going to the wrong port

Hi gang, Got a strange problem with a NAT'd device that's trying to connect to FS. The first REGISTER arrives, without auth, and FS responds with 401 Unauthorized to the correct port on the external IP address of the firewall. However when the second attempt to REGISTER, this time with auth, comes in, FS responds with 200 OK to the local SIP port specified on the device. The device obviously doesn't get the 200 OK so keeps attempting to register. Any ideas? Tried sip-force-contact but that doesn't seem to help. Alex