Problem with UPNP_E_UNSUBSCRIBE_UNACCAPTED [-302]

Dear All:
                I trace the sample code with upnp_tv_device and upnp_tv_ctrlp.
                when I key in the exit command in upnp_tv_device program.
                the upnp_tv_ctrlp will recive the UPNP_DISCOVERY_ADVERTISEMENT_BYEBYE
                message send by upnp_tv_device and it cause the action with unsubscribe in upnp_tv_ctrlp.
                but, it always cause the  UPNP_E_UNSUBSCRIBE_UNACCAPTED [-302] error
                when upnp_tv_ctrlp execution the UpnpUnSubscribe( ) function.
                Do there have anybody know which situation will cause this error in the program!!
                                                                                                                            
thanks!!

                PS: the sample code is publish with libupnp-1.2.1.tar.gz