[bug#3903] Fixed edge effects in _update_object function.

            client_id = parent['id']

        if tags is not None:

            tags = set(tags)

            tags -= set(user_tags)

        if tags_novalue is not None:

            tags_novalue = set(tags_novalue)

            tags_novalue -= set(user_tags)

        try:

            client = self._server.get_connection(client_id)

        except KeyError:

            pass

            # The client is not connected, we need to keep only unttlised tags:

            for name in obj.keys():

                if (obj['id'], name) in self._ttls:

                    del obj[name]

        else:

            # The client is connected:

            if parent is None: