Symmetric Latching and media port changes

I have an interesting situation with a customer using an Avaya PBX. I currently have symetric latching enabled, with restricted set to 'none'. 

 

Lets say the call starts off with the Avaya sending RTP to the SBC port 20,000 as adverstised in our SDP. The Avaya is sourcing this from a different IP and port  than they list in their SDP ( behind nat). With symetric latching, that should be fine, as we latching onto that first packet. 

 

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Example : 

 

Customer : 

SDP c = 1.1.1.1 

m = 61252 

RTP originates from 2.2.2.2 port 21500

 

Me:

SDP c = 9.9.9.9

m = 20000

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Often within 20-50 RTP packets into the call, the Avaya starts sending RTP from a different port AND to a different destination port on our SBC.