[Serusers] Please HELP: TM Module Question

Hi All. I have a problem which I think is a Sonus issue, but I need to make sure before I blame someone else for what could be my problem. The issue is related to re-INVITE messages from a Sonus PSTN gateway to my SER-0.9.1 sip proxy. Sometimes the Sonus box sends us a retransmitted re-INVITE for which SER just sent a 200OK. It occasionally does this even considering we originally reply with a 100Try message. So what SER then does is forwards the retransmitted re-INVITE to the SIP UA, but the SIP UA ignores this re-INVITE because it just sent a 200OK for the original re-INVITE. SER keeps trying to send the re-INVITE to the SIP UA until it times out, then it replies to the Sonus GW with a 407 Request Timeout and then Sonus disconnects the call and sends SER a BYE message. Now what I didn't mention yet is that when ser sends a 200OK response back to the Sonus box in reponse to the original re-INVITE, rather than getting an ACK back from Sonus we get a retransmitted re-INVITE and then we get the ACK. So since the SIP UA is smart enough to know not to response to the retransmitted re-INVITE, shouldn't SER also be smart enough and just absorb it rather than relaying it to the SIP UA? Anyhow a picture is worth a million words so here is a SIP message log that begins with a re-INVITE from the Sonus GW. NOTE 1: SER is located behind a Cisco 3600 so the ALG functionality in the 3600 has rewritten all the IP address (ie, the 10.3.0.0 network). NOTE 2: This problem seems to be random. Some calls are very short and others are very long before the disconnect happens - and still others are perfectly fine for the call duration. NOTE 3: Sonus sends SER a re-INVITE every two minutes. Can anyone please confirm that ser has indeed handled this re-INVITE properly and that Sonus is actually incorrectly processing calls? Is there a way to hack a band-aide here in the event that the problem is Sonus and they will not fix their side? Regards, Paul