[Serusers] Claims of ser-0.9 RFC3261 Violation

I just spoke with an enginee from a manufacturer of the WorldAccxx telephone adapter and he told me that my SIP proxy was in voliation of RFC3261. Below is a SIP registration against my ser-0.9 proxy. I'm using media proxy for NAT traversal and he says that my 200 OK is not valid and therefore their IAD disregards the 200 OK response. The problem he claims is with the <Contact:> header in the 200 OK. SER has rewritten the contact becase his IAD is NATed. Should I not be doing this? The actual problem is that when their IAD is NATed the device looses its registration with ser because (they claim) that the REGISTER message they send has a <Contact> header iwith a different IP than what ser sends back in the 200 OK message. They referenced section 10.2.4 and 19.1.4 in RFC3261. Can anyone confirm or reject their claims? Please help. Paul REGISTER sip:sip.mycompany.com:5060 SIP/2.0 Via: SIP/2.0/UDP 192.168.0.180;branch=z9hG4bKbb013e10d Max-Forwards: 70 Content-Length: 0 To: Accxx <sip:1000@sip.mycompany.com:5060> From: Accxx <sip:1000@sip.mycompany.com:5060>;tag=1eb7db0b344ac92 Call-ID: bd4da0ebfe98297597243a92b1b0f868(a)192.168.0.180 CSeq: 392547129 REGISTER Contact: Accxx <sip:1000@192.168.0.180;user=phone>;expires=200 Allow: NOTIFY Allow: REFER Allow: OPTIONS Allow: INVITE Allow: ACK Allow: CANCEL Allow: BYE User-Agent: WATA200 Callctrl/1.5.1.1 MxSF/v3.2.6.26 SIP/2.0 100 Trying Via: SIP/2.0/UDP 192.168.0.180;branch=z9hG4bKbb013e10d;rport=36323;received=65.77.37.2 To: Accxx <sip:1000@sip.mycompany.com:5060> From: Accxx <sip:1000@sip.mycompany.com:5060>;tag=1eb7db0b344ac92 Call-ID: bd4da0ebfe98297597243a92b1b0f868(a)192.168.0.180 CSeq: 392547129 REGISTER Content-Length: 0 SIP/2.0 401 Unauthorized Via: SIP/2.0/UDP 192.168.0.180;branch=z9hG4bKbb013e10d;rport=36323;received=65.77.37.2 To: Accxx <sip:1000@sip.mycompany.com:5060>;tag=bf952ed189d8425c881b09485aa0b6f1.bdad From: Accxx <sip:1000@sip.mycompany.com:5060>;tag=1eb7db0b344ac92 Call-ID: bd4da0ebfe98297597243a92b1b0f868(a)192.168.0.180 CSeq: 392547129 REGISTER WWW-Authenticate: Digest realm="sip.mycompany.com", nonce="42025161902f6f6af11f01f0a93ad2877e606bbc" Content-Length: 0 REGISTER sip:sip.mycompany.com:5060 SIP/2.0 Via: SIP/2.0/UDP 192.168.0.180;branch=z9hG4bK88fcb4e76 Max-Forwards: 70 Content-Length: 0 To: Accxx <sip:1000@sip.mycompany.com:5060> From: Accxx <sip:1000@sip.mycompany.com:5060>;tag=1eb7db0b344ac92 Call-ID: bd4da0ebfe98297597243a92b1b0f868(a)192.168.0.180 CSeq: 392547130 REGISTER Contact: Accxx <sip:1000@192.168.0.180;user=phone>;expires=200 Allow: NOTIFY Allow: REFER Allow: OPTIONS Allow: INVITE Allow: ACK Allow: CANCEL Allow: BYE Authorization:Digest response="18aabe984a6d89cc537cec9ce43b198d",username="1000",realm="sip.mycompany.com",nonce="42025161902f6f6af11f01f0a93ad2877e606bbc",uri="sip:sip.mycompany.com:5060" User-Agent: WATA200 Callctrl/1.5.1.1 MxSF/v3.2.6.26 SIP/2.0 100 Trying Via: SIP/2.0/UDP 192.168.0.180;branch=z9hG4bK88fcb4e76;rport=36323;received=65.77.37.2 To: Accxx <sip:1000@sip.mycompany.com:5060> From: Accxx <sip:1000@sip.mycompany.com:5060>;tag=1eb7db0b344ac92 Call-ID: bd4da0ebfe98297597243a92b1b0f868(a)192.168.0.180 CSeq: 392547130 REGISTER Content-Length: 0 SIP/2.0 200 OK Via: SIP/2.0/UDP 192.168.0.180;branch=z9hG4bK88fcb4e76;rport=36323;received=65.77.37.2 To: Accxx <sip:1000@sip.mycompany.com:5060>;tag=bf952ed189d8425c881b09485aa0b6f1.5e63 From: Accxx <sip:1000@sip.mycompany.com:5060>;tag=1eb7db0b344ac92 Call-ID: bd4da0ebfe98297597243a92b1b0f868(a)192.168.0.180 CSeq: 392547130 REGISTER Contact: <sip:1000@65.77.37.2:36323;user=phone>;expires=200, <sip:1000@65.77.37.2:36235;user=phone>;expires=3 Content-Length: 0