There is a setting "Follow RTP" (in reg_rtpsettings.htm) for that. I guess this one is turned on? Then the PBX should follow the RTP. You should see a message like "Tuning to new SSRC from xxx" (log level 5, media).
The message "Source address for sip:xxxxx has changed from tls:192.168.x.y:39992 to tls:80.226.x.x:43321" is not related to RTP, this is about the registration, it is actually pretty useless if you have mobile device that change the IP address all the time.