Unexpected API Error is returned, when trying to add fixed IP to an instance in ERROR state

A negative test case returns an Unexpected API Error, while there is more detailed message in nova-api.log:

2016-01-12 15:12:49.357 22446 ERROR nova.api.openstack.extensions NovaException: Unable to find host for Instance efbbb0cb-fe5f-4047-868e-69305536bcd4
2016-01-12 15:12:49.391 22446 INFO nova.osapi_compute.wsgi.server [req-e22c4d4d-37c8-443d-8038-15ec3f47d01a 7f0fce3a7e3f479b9933eff3df35649d 65d0c9e644ac4c518e76bc9922ef47ee - - -] 192.168.0.2 "POST /v2/65d0c9e644ac4c518e76bc9922ef47ee/servers/efbbb0cb-fe5f-4047-868e-69305536bcd4/action HTTP/1.1" status: 500 len: 428 time: 0.3730938

Steps to reproduce:
1. Create net01: net01__subnet, 192.168.1.0/24:
neutron net-create net01
neutron subnet-create net01 192.168.1.0/24 --enable-dhcp --name net01__subnet
2. Boot an instance vm1 in net01 with incorrect compute node:
NET_ID=$(neutron net-list | grep 'net01' | awk '{print $2}')
nova boot --flavor m1.micro --image TestVM --nic net-id=$NET_ID --security-groups default --availability-zone nova:<some-controller-node.domain.tld> vm1
3. Check that the instance is in ERROR state now and isn’t assigned to any host:
nova show vm1 | grep OS-EXT-SRV-ATTR:host && nova show vm1 | grep status
| OS-EXT-SRV-ATTR:host | - |
| status | ERROR
4. Try to assign fixed IP to the instance vm1 and ensure that it returns an error:
nova add-fixed-ip vm1 $NET_ID

The expected result:
An error message, something like " Returning 409 to user: Cannot 'attach_interface' instance efbbb0cb-fe5f-4047-868e-69305536bcd4 while it is in vm_state error " appears

The actual result:
ERROR (ClientException): Unexpected API Error. Please report this at http://bugs.launchpad.net/nova/ and attach the Nova API log if possible.
<class 'nova.exception.NovaException'> (HTTP 500) (Request-ID: req-e22c4d4d-37c8-443d-8038-15ec3f47d01a)
appears

Nova version - http://paste.openstack.org/show/483603/
nova-api logs for faulty instance - http://paste.openstack.org/show/483611/