Comment 1 for bug 1381886

it's neutron's problem.
the operation in bug description is floating ip re-assignment, this can depart into two steps, disassociate from origin port, associate to new port; when re-assign floating ip, network changes happened on two(origin, new) instance's port, but neutron only send event for new instance port;
add code ensure neutron will first send event for origin/disassociate one, then send event for new/associate one, will fix this.