Another manifestation of the bug has been discovered.
It's not severe now, but leaves traces in the log file which better be avoided:

2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db Traceback (most recent call last):
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/neutron/db/agentschedulers_db.py", line 269, in remove_networks_from_down_agents
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     notify=False)
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/neutron/db/agentschedulers_db.py", line 351, in remove_network_from_dhcp_agent
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     query.delete()
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 2670, in delete
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     delete_op.exec_()
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 896, in exec_
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     self._do_pre_synchronize()
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 958, in _do_pre_synchronize
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     eval_condition(obj)]
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/evaluator.py", line 90, in evaluate
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     value = sub_evaluate(obj)
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/evaluator.py", line 115, in evaluate
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     left_val = eval_left(obj)
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/evaluator.py", line 72, in <lambda>
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     return lambda obj: get_corresponding_attr(obj)
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/attributes.py", line 239, in __get__
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     return self.impl.get(instance_state(instance), dict_)
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/attributes.py", line 589, in get
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     value = callable_(state, passive)
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/state.py", line 424, in __call__
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     self.manager.deferred_scalar_loader(self, toload)
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/loading.py", line 614, in load_scalar_attributes
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db     raise orm_exc.ObjectDeletedError(state)
2015-04-07 15:41:44.857 19946 TRACE neutron.db.agentschedulers_db ObjectDeletedError: Instance '<NetworkDhcpAgentBinding at 0x7f53eb7092d0>' has been deleted, or its row is otherwise not present.