[Serusers] HELP: Why does SER not absorb this re-INVITE?

Hi all. I have a big problem and I really need some help. re-INVITE messages are not properly processed during __random__ call durations. Sometimes a call can exceed 1 hour and sometimes a call is only two minutes, then ser improperly processes a re-INVITE and a 408 Request Timeout is sent back to the Sonus GW, which then drops the call. Attached is a partial call log that begins with a re-INVITE. NOTE: this is __NOT__ the first re-INVITE of this call. This call lasted more than 30 minutes and re-INVITEs were sent on a 2 minute interval. Anyhow, the re-INVITE is processed and the SIP phone ACKed it, however another re-INVITE got sent from the Sonus GW which ser incorrectly tried to send to the SIP UA. The SIP UA correctly ignored the re-INVITE since it just ACKed it. SER retransmits the re-INVITE to the SIP UA until the fr_invite timer expires, then it sends a 408 Request Timeout back to the Sonus GW, which then disconnects the call and sends ser a BYE message. Is this a bug in the ser TM module? Shouldn't ser just absorb the re-INVITE since it just ACKed it rather than trying to send the re-INVITE to the SIP UA? The Sonus guys say that this is an error in the ser SIP stack. Please help. I'm really stuck with this one. Regards, Paul