Comment 2 for bug 1789846

this code is suspected:

        if agent_active_ports == 1 or self.agent_restarted(context):
            # First port activated on current agent in this network,
            # we have to provide it with the whole list of fdb entries
            agent_fdb_entries = self._create_agent_fdb(port_context,
                                                       agent,
                                                       segment,
                                                       network_id)

            # And notify other agents to add flooding entry
            other_fdb_ports[agent_ip].append(const.FLOODING_ENTRY)

            if agent_fdb_entries[network_id]['ports'].keys():
                self.L2populationAgentNotify.add_fdb_entries(
                    self.rpc_ctx, agent_fdb_entries, agent_host)

where agent_active_ports == 2 in our case so the agent is not provided with the whole list of fdb entries.

changing to "if agent_active_ports in (1,2)" fixed the issue.
Patch to follow.