FYI - I just hit the same.
IMO the most likely case to hit this is by running Trusty with the Ubuntu Cloud Archive. That brings in a newer libvirt and that way makes it hit the same issue as you had for utopic here.
@Robie - do you think you would consider this for Trusty?
Also I love "As a temporary workaround", nothing endures as long as these :-)
FYI - I just hit the same.
IMO the most likely case to hit this is by running Trusty with the Ubuntu Cloud Archive. That brings in a newer libvirt and that way makes it hit the same issue as you had for utopic here.
@Robie - do you think you would consider this for Trusty?
Also I love "As a temporary workaround", nothing endures as long as these :-)