Comment 13 for bug 1665698

Even with that things are still working correctly for me:
Here the "no" case re-ran with the device being set up externally.

$ tunctl -t manualdevname
$ ip link set manualdevname up
$ ip link set manualdevname master virbr0

For the config:
    <interface type='ethernet'>
      <mac address='52:54:00:18:0d:a3'/>
      <target dev='manualdevname'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </interface>

This case worked prior and after the fix in 1.3.1-1ubuntu10.8 for me then.