Audio sent from two different sources - second ignored until reinvite

I have a scenario where the SBC receives two different RTP flows related to the same Invite/SDP.   The one that arrives first...the SBC latches onto.   That source stops sending shortly after.   The desired RTP continues from the second IP...but isn't passed along thru the SBC.   I believe the switch from the first IP to the second IP is the invocation of some DSP resources further in the network that happens after the RTP starts being transmitted from first IP.   There is no signaling event to trigger this change.    Later in the flow...the call is put on hold and resumed (signaling