[Users] BYE relay issue

Dear sir, We install 3 openser 1.1.0 in public internet, and we find a BYE relay issue to caller SIP UA. UA(a)-------Proxy1 --------Proxy2 ----Proxy 3 ---------UA(b) We make call from UA(a) to UA (b), if UA(b) send Bye first, UA(a) can not get Bye. The packet is from Proxy2 to Proxy1 as following BYE sip:1.2.3.4:5060;nat=yes;ftag=ooqjvbi7ql;lr=on SIP/2.0 Record-Route: <sip:5.6.7.8;lr=on;ftag=as1b41fbeb> Record-Route: <sip:5.6.7.8;lr=on;ftag=as1b41fbeb> Via: SIP/2.0/UDP 5.6.7.8;branch=z9hG4bKc74c.bd89ce13.0 Via: SIP/2.0/UDP 5.6.7.8;branch=z9hG4bKc74c.ad89ce13.0 Via: SIP/2.0/UDP 100.200.100.200;branch=z9hG4bKc74c.321ef5e3.0 Via: SIP/2.0/UDP 100.200.100.199:5060;branch=z9hG4bK75e8d6f3;rport=5060 From: <sip:0908900000@sip.edu.tw;user=phone>;tag=as1b41fbeb To: "0909802020 kl" <sip:0909802020@sip.edu.tw>;tag=ooqjvbi7ql Call-ID: 3c275da915f9-iylvmp2wjuh0@snom360-00041323058B CSeq: 102 BYE User-Agent: Gentrice_IPPBX Max-Forwards: 67 Content-Length: 0 Then bye is looping in proxy1. BYE sip:1.2.3.4:5060;nat=yes;ftag=ooqjvbi7ql;lr=on SIP/2.0 Record-Route: <sip:5.6.7.8;lr=on;ftag=as1b41fbeb> Record-Route: <sip:5.6.7.8;lr=on;ftag=as1b41fbeb> Via: SIP/2.0/UDP 1.2.3.4;branch=z9hG4bKc74c.1714a4e7.0 Via: SIP/2.0/UDP 5.6.7.8;branch=z9hG4bKc74c.bd89ce13.0 Via: SIP/2.0/UDP 5.6.7.8;branch=z9hG4bKc74c.ad89ce13.0 Via: SIP/2.0/UDP 100.200.100.200;branch=z9hG4bKc74c.321ef5e3.0 Via: SIP/2.0/UDP 100.200.100.199:5060;branch=z9hG4bK75e8d6f3;rport=5060 From: <sip:0908900000@sip.edu.tw;user=phone>;tag=as1b41fbeb To: "0909802020 kl" <sip:0909802020@sip.edu.tw>;tag=ooqjvbi7ql Call-ID: 3c275da915f9-iylvmp2wjuh0@snom360-00041323058B CSeq: 102 BYE User-Agent: Gentrice_IPPBX Max-Forwards: 66 Content-Length: 0 We used to use default script for proxy1, but the same... And we do record_route, loose_route relay as well. Anyone know what happen? best regards Thrli