[USR-TC] problem with MOH

MOH is not working with me: when another call is received while the modem is connected to TC1000, the network behind TC1000 becomes unreachable. if the calling party stops ringing in a short time (less the 1 min) the connection "may" be restored. But in the case when I answer the call or I reject it, the connection will be lost permanently and the modem will be disconnected in approximately 1 minute. NOTE: V.92 is fully enabled and Modem On Hold Timeout is more then enough from the DSP side. Any help/tip is much appreciated.