Richard Fuchs writes:
Possibly it's because of the non-standard RTCP port in the answer. Technically this is supported but the implementation is more of a hack than anything else for the time being.
looks like the rtpc port number in 200 ok is not "non-standard" anymore. from rfc 3605 dated october 2003:
The SIP messages use the encoding defined in SDP [RFC2327] to describe the IP addresses and TCP or UDP ports used by the various media. Audio and video are typically sent using RTP [RFC3550], which requires two UDP ports, one for the media and one for the control protocol (RTCP). SDP carries only one port number per media, and states that "other ports used by the media application (such as the RTCP port) should be derived algorithmically from the base media port." RTCP port numbers were necessarily derived from the base media port in older versions of RTP (such as [RFC1889]), but now that this restriction has been lifted, there is a need to specify RTCP ports explicitly in SDP.
-- juha