Thanks everybody for your comments.
I can confirm all your findings. The problem is the router-interface port.
I analyzed the logs of this run http://logs.openstack.org/91/114691/6/experimental/check-tempest-dsvm-neutron-dvr/73cff0a/

The router interface is 86c6f7a4-31e6-4cd4-837a-68843730c101

From the q-agt log we see that the router interface is not present in the interface list and it's marked as removed:

2014-08-21 04:42:52.026 28137 DEBUG neutron.plugins.openvswitch.agent.ovs_neutron_agent [req-74f7c36e-7acb-4398-995c-a5d9c3e5ad98 None] Starting to process devices in:{'current': set([u'fe074629-227d-42e4-8b16-21f2efc0e8c7', u'4423ca10-d95e-4ce7-abc8-25ce4bd308fa', u'c3349086-3b0d-49fe-85ce-c2ae7ce55fcc', u'a376b867-5843-47a4-a158-5157e441d937', u'0a82de5e-e62f-475c-bc9c-ed115bd58afd', u'cd5c3035-2cd5-4e4c-93c7-d20075972120']), 'removed': set([u'86c6f7a4-31e6-4cd4-837a-68843730c101']), 'added': set([u'4423ca10-d95e-4ce7-abc8-25ce4bd308fa'])} rpc_loop /opt/stack/new/neutron/neutron/plugins/openvswitch/agent/ovs_neutron_agent.py:1400


2014-08-21 04:42:56.116 28137 INFO neutron.plugins.openvswitch.agent.ovs_neutron_agent [req-74f7c36e-7acb-4398-995c-a5d9c3e5ad98 None] Attachment 86c6f7a4-31e6-4cd4-837a-68843730c101 removed


Then the interface is detected again:
2014-08-21 04:42:59.293 28137 DEBUG neutron.plugins.openvswitch.agent.ovs_neutron_agent [req-74f7c36e-7acb-4398-995c-a5d9c3e5ad98 None] Starting to process devices in:{'current': set([u'fe074629-227d-42e4-8b16-21f2efc0e8c7', u'4423ca10-d95e-4ce7-abc8-25ce4bd308fa', u'c3349086-3b0d-49fe-85ce-c2ae7ce55fcc', u'a376b867-5843-47a4-a158-5157e441d937', u'86c6f7a4-31e6-4cd4-837a-68843730c101', u'0a82de5e-e62f-475c-bc9c-ed115bd58afd', u'cd5c3035-2cd5-4e4c-93c7-d20075972120']), 'removed': set([]), 'added': set([u'86c6f7a4-31e6-4cd4-837a-68843730c101'])} rpc_loop /opt/stack/new/neutron/neutron/plugins/openvswitch/agent/ovs_neutron_agent.py:1400

2014-08-21 04:43:00.332 28137 DEBUG neutron.plugins.openvswitch.agent.ovs_neutron_agent [req-74f7c36e-7acb-4398-995c-a5d9c3e5ad98 None] Processing port: 86c6f7a4-31e6-4cd4-837a-68843730c101 treat_devices_added_or_updated /opt/stack/new/neutron/neutron/plugins/openvswitch/agent/ovs_neutron_agent.py:1090

This operation fails because:
2014-08-21 04:43:00.809 28137 WARNING neutron.plugins.openvswitch.agent.ovs_neutron_agent [req-74f7c36e-7acb-4398-995c-a5d9c3e5ad98 None] Device 86c6f7a4-31e6-4cd4-837a-68843730c101 not defined on plugin

If we check in the q-srv log we see:

2014-08-21 04:43:00.314 28081 DEBUG neutron.plugins.ml2.db [req-74f7c36e-7acb-4398-995c-a5d9c3e5ad98 None] No binding for DVR port 86c6f7a4-31e6-4cd4-837a-68843730c101 with host devstack-trusty-hpcloud-b5-1583220 get_dvr_port_binding_by_host /opt/stack/new/neutron/neutron/plugins/ml2/db.py:222
2014-08-21 04:43:00.315 28081 ERROR neutron.plugins.ml2.plugin [req-74f7c36e-7acb-4398-995c-a5d9c3e5ad98 None] Binding info for DVR port 86c6f7a4-31e6-4cd4-837a-68843730c101 not found

At this point the port is set as dead using the tag 4095

2014-08-21 04:43:01.057 28137 DEBUG neutron.agent.linux.utils [req-74f7c36e-7acb-4398-995c-a5d9c3e5ad98 None] Running command: ['sudo', '/usr/local/bin/neutron-rootwrap', '/etc/neutron/rootwrap.conf', 'ovs-vsctl', '--timeout=10', 'set', 'Port', 'qr-86c6f7a4-31', 'tag=4095'] create_process /opt/stack/new/neutron/neutron/agent/linux/utils.py:48