[OpenSER-Users] Formation of ACKs?

Hello all, I'm having problems with ACKs not beeing matched to an ongoing call, thus OpenSER resends a 487 many times. My question is, would OpenSER deny an ACK depending on how the headers are sorted in the packet? Eg. if the VIA-header is found at the end of the packet? How does it actually match the 487 and the ACK? Packet from proxy that OpenSER doesn't seem to match: User-Agent: hotsip-transactron Max-Forwards: 70 Content-Length: 0 To: <sip:123456@domain2.se>;tag=1499854882 From: "PBX" <sip:654321@domain1.se>;tag=as2fa86da4 Call-ID: 22079ed445536bea109aefc410164bb5(a)domain1.se CSeq: 103 ACK Via: SIP/2.0/UDP 192.168.0.1:5060;branch=z9hG4bK-81056ef2a1e003b87474dfaa6a5e7959;rport=5060 Br, /Tobias