Unregister issue

1. Brekeke Product Name and Version:Brekeke SIP Server, Version 3.8.6.4

2. Java version:

3. OS type and the version:Windows 10

4. UA (phone), gateway or other hardware/software involved:

5. Your problem:

My softphone is behind NAT. Firstly it registers to Sip Server with Contact header which has local IP. Then it detects IP change and sends REGISTER with two Contact headers. One is for UNregister the contact defined with local IP(by setting expires param is zero). Other one is for register the contact defined with public IP.

The REGISTER message with two Contact header:
REGISTER sip:xxx:xx;transport=tls SIP/2.0
***
Call-ID: zQwMyXU8RH3tD6ktlTXH8wAOoKixCR.P
CSeq: 14404 REGISTER
Contact: <sip:7701@public-ip:public-port;transport=TLS;ob>
Contact: <sip:7701@local-ip:local-port;transport=TLS;ob>;expires=0;reg-id=1;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000008845ff7>"
Expires: 300
***


But BSS responses the REGISTER message with two Contact and does not unregister the account which contact is defined with local IP.

Is there a way to solve this issue?


BSS OK response:
SIP/2.0 200 OK
***
Call-ID: zQwMyXU8RH3tD6ktlTXH8wAOoKixCR.P
CSeq: 14404 REGISTER
Server: Brekeke SIP Server rev.501 Evaluation
Contact: <sip:7701@public-ip:public-port;transport=TLS;ob>;expires=300;q=1.0
Contact: <sip:7701@local-ip:local-port;transport=TLS;ob>;expires=300;q=1.0;reg-id=1;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000008845ff7>"
***

Which SIP phone client product is it?
Can you send two separate REGISTER requests? one is for un-registering and another is for registering.

The client is developed with pjsip. Pjsip supports separate request sending. I wanted to ask if there is a server-side config.
Thanks