[Users] UA behind NAT puts public IP in Contact, Via - help

Hi, Few days ago I presented UA that sends public IP in "Contact" and "Via" HF, when it is behind NAT. It is in private LAN but it learns its public IP and every SIP request will contain public addresses. It ruins NAT traversal effort, inluding nathelper + rtpproxy. I cannot properly detect NAT-ed user neither by "Via" nor "Contact" check. As a result people with various modems get angry and are reporting to me all those "I have no audio" problems. Or they cannot even register at all, if they have partcularly stupid NAT. What is your advice? Vendor knows about issue but doesn't see problem. Of course I can enable NAT traversal by "User-Agent" HF check, but 90% of those UAs are NOT behind NAT... -- Regards, Arek Bekiersz