Is possible that SER send a reply (ex: 487 request cancelled) at the expiration of the "fr_inv_timer" and this reply cant be handled by the "t_on_reply" command ??? I see this when a call expire fr_inv_timer (calee dont answer) and cause the imposibility to instruct the mediaproxy to end the session.

My ser.cfg like to be ok, when i cancel the call (after expire of fr_inv_timer) the CANCEL is handled by onreply_route and after eval the status i can do a end_media_proxy();