Errors in MGCP do not propagate back to MNCC gsm_subscriber_conn state machine
TC_mo_crcx_ran_reject shows that if the CRCX during call setup fails the call control state machine just stalls. The MGCP code handles that case and clears all connections on the endpoint.
The call control side is never notified of the failure and so the connection just hangs half open at that stage.
See handle_error() and the caller mgw_crcx_ran_resp_cb() in libmsc/msc_mgcp.c
In case of an error the MGCP code should make sure the call is released to the phone side and also notify the (external) mncc.