Previously, when a network device was removed from the system through a means that was not VDSM, VDSM recognized that the device was removed and it stopped reporting the device to the engine. But libvirt still held a reference to the removed device. If the user attempted to create the device again, the attempt failed because libvirt still holds a reference to the non-existent device.
Broken networks are now removed from libvirt before new networks are set up. The re-creation of broken networks no longer causes exceptions.