[Serusers] Sip Proxy behind Nat.

Hi Users, I am Using SER-0.9.6 on a public ip and using another sip-proxy(not SER) behind the NAT. and when the users who registerd to Sip-proxy which is behind NAT,, calls to the users who registered to public domain SER.. call is being established . but when hunging the phone the SER is not sending "BYE" messages to the NAT device it is sending to the Sip-proxy (not SER) that is for a private IP . so even when i hung the call from the Nated Sip proxy ,SER is getting messages through NAT but again SER is not sending "BYE" messages to other party its sending back to the nated sip-proxy having private IP , so the messages are going in a wrong direction and is being wasted . It looks like this is a BUG in SER , i would take this oppurtunity to report this. If this is not a bug please send me the suggestions ..... To solve my problem. thank you. regards, Ravi.