Reason header ends call (Q.850 cause code 4)

One called party is returning a Reason Header in 183 w/SDP with cause code 4 (special tone) and Asterisk (version 16 using chan_sip) immediately issues a CANCEL to called party. I don’t think it is a tone that indicates call can’t be setup and called party side says they send 200 OK right after that but Asterisk has already ended the call. Is there anyway to disable this behaviour? Ignore incoming Reason header with Q.850 cause code 4?

I told them that this is normal as usually Reason header indicates call release, but they insist this is not a case that should release call. Any ideas?

In what circumstances is an SIT being sent. I’m not aware of any use of SIT other than for failed calls.

I just assumed that too based on: Cause 4 Send special information tone - This cause indicates that the called party cannot be reached for reasons that are of long term nature and that the special information tone should be returned to the calling party.

I will ask them what info they are trying to convey or just capture the rtp sent and listen myself. I also glanced thru the asterisk code and noticed that cause code 4 is not even defined so I guess it falls into the category of undefined. I have also asked them to remove the Reason header, but so far they are sticking with the story that they can’t do it.