Comment 6 for bug 1246128

The probable source of error is

                send_up(Datagram(dg, dg.offset() + msg.serial_size()),
                        ProtoUpMeta(msg.source_uuid()));
                p->set_tstamp(gu::datetime::Date::now());

It is possible that delivering a message up in the stack will cause p to be erased from proto_map_. Fix would be simply changing the order of operations and nulling p to make sure that it is not dereferenced after send_up() call.