We have Yealink T26P and T41P phones and when we do an introduced call transfer of an incoming call the external caller hears the music on hold over the call. ie the music on hold doesnt turn off when the call has been picked up. This happens when you press either the soft "trans" under the screen or the hard key "tran" of the 6 buttons. Thus our system doesnt allow us to transfer calls at the moment. What do we do?