The mutex of server_vc is not set while server_session reuse

NetAccept got a client_vc and call new_ProxyMutex() to assign a mutex.
And the HttpClientSession, HttpSM, HttpServerSession, server_vc also share the same mutex.

The HttpServerSession and server_vc will put into ServerSessionPool and may assign to next new client_vc.

The HttpSM::attach_server_session() only set the mutex of HttpServerSession to the mutex of HttpSM after get a HttpServerSession from ServerSessionPool.
But it forget to set the mutex of server_vc to the mutex of HttpSM.

void
HttpSM::attach_server_session(HttpServerSession *s)
{
  hsm_release_assert(server_session == NULL);
  hsm_release_assert(server_entry == NULL);
  hsm_release_assert(s->state == HSS_ACTIVE);
  server_session = s; 
  server_session->transact_count++;

  // Set the mutex so that we have something to update
  //   stats with
  server_session->mutex = this->mutex;

But I can not found any issue, Is it by design?
Or it is hard to locate the problem, due to my limited knowedge on HttpSM.