[SR-Users] outbound loose routing question

Dear list I'm trying to route using the loose_route() method for an ACK message of an INVITE. the ACK message contains a Route header field with the outbound proxy address (which is the server processing this message - aka "myself") and a flow token to the UAC. but the routing is failed because the process_outbound() function in loose.c deliberatly ignores my flow-token because of the condition in loose.c:522 which is: else if (!ip_addr_cmp(&rcv->src_ip, &_m->rcv.src_ip || rcv->src_port != _m->rcv.src_port). I don't understand why i cannot use this flow token to send the ACK back to the UAC... Thanks in advance...