Why does a volume appear twice on the admin console?

If you reformat a volume using the Utility menu, a new volume id will be generated by the cluster for each reformatted volume.  The cluster will still remember the previous volume id, however, and will show those volumes as offline since they are no longer present in the cluster.  Cluster memory of missing volume ids is necessary and beneficial as this is how failed volumes are discovered so that any content associated with the missing volume can be recovered.  The previous volumes will no longer display after a reboot.