We recently had an issue wherein a job owner added a co-owner by entering their display name ("LName, FName" in our case). This appeared to work. The co-owner was correctly displayed on the ownership page, including resolution of their email address. However the co-owner did not acquire the permissions that a co-owner should receive. They were unable to view or edit the job configuration for example. When we removed them and re-added them as "fname.lname", which is their active directory login, (we use the "Active Directory" security realm) things worked. It seems that either both approaches should work (probably not the best solution as display name can be ambiguous) or there needs to be a clear error or other indicator when a non-valid user-id is entered as a co-owner.