[Serusers] Ser & RTPproxy does not change the SDP vodeo port.

hi, I'm using ser 0.9.7 and RTPproxy 1.1 on diffrent servers. the ser.cfg is the nat-rtpproxy.cfg from the iptel site. I have 2 grandstream GXV-300 devices, each behind diffrent NAT, this setup is working fine for voice and RTP is relayed through the rtpproxy properly. The problem is that the video is not working, when ser gets the invite from device A and send it to device B, it change the audio port only but leave the video port the same as the port he got from device A. I'm not sure if it is an issue with the RTPproxy or the nat-helper module. any idea how to debug / resolve? do you aware of other versions of ser/rtpproxy that this setup should work with video? Thanks! Amos