Hello,
Please refer to sip trace:
http://pastebin.org/86010.
On LINE 294, PSTN sends the Re-INVITE
On LINE 378, REGISTRAR sends 200 OK to SIP SBC (with RFC 1918 Address, that
is being relayed from the UAC that also sends this same address upon 200 OK
of the Re-Invite).
Let me know if this makes sense, this trace was taken on the SBC.