Comment 2 for bug 1815585

I did some initial investigation on this. It looks that nova-compute received information to detach interface and told Libvirt to detach it:
http://logs.openstack.org/91/635691/1/gate/neutron-tempest-plugin-scenario-linuxbridge/3cc34c4/controller/logs/screen-n-cpu.txt.gz#_Feb_12_09_16_39_511365

So neutron-linuxbridge-agent found this event and removed port here: http://logs.openstack.org/91/635691/1/gate/neutron-tempest-plugin-scenario-linuxbridge/3cc34c4/controller/logs/screen-q-agt.txt.gz#_Feb_12_09_16_39_951803

And there is also matched even in neutron-server to switch port to DOWN:
http://logs.openstack.org/91/635691/1/gate/neutron-tempest-plugin-scenario-linuxbridge/3cc34c4/controller/logs/screen-q-svc.txt.gz#_Feb_12_09_16_39_973353

According to that it looks that all was fine and port should be set to DOWN but for some reason port status in response from neutron looked like:

{"port":{"id":"7b6ccd25-cc09-41a3-ba4b-b23169819c11","name":"","network_id":"0976b2ae-c8c4-4d3c-a1df-bbbded993f28","tenant_id":"5ecab117503f46b7af1a7e6c3707c2e7","mac_address":"fa:16:3e:60:df:15","admin_state_up":true,"status":"ACTIVE","fixed_ips":[{"subnet_id":"ad2dc4a4-1b02-45f9-9042-60b5788cd2d9","ip_address":"10.1.0.12"}],"device_id":"","device_owner":"","allowed_address_pairs":[],"extra_dhcp_opts":[],"security_groups":["fd9de87a-7f94-4def-ae63-871b5f220abc"],"description":"","binding:vnic_type":"normal","port_security_enabled":true,"propagate_uplink_status":false,"qos_policy_id":null,"dns_name":"","dns_assignment":[{"ip_address":"10.1.0.12","hostname":"host-10-1-0-12","fqdn":"host-10-1-0-12.openstackgate.local."}],"dns_domain":"","ip_allocation":"immediate","tags":[],"created_at":"2019-02-12T09:15:16Z","updated_at":"2019-02-12T09:16:47Z","revision_number":9,"project_id":"5ecab117503f46b7af1a7e6c3707c2e7"}}

It is here:
http://logs.openstack.org/91/635691/1/gate/neutron-tempest-plugin-scenario-linuxbridge/3cc34c4/controller/logs/tempest_log.txt.gz#_2019-02-12_09_16_50_122

Please note that port has empty device_id but status ACTIVE