We have several users that when they login to Phabricator with their AD credentials they get prompted to register again. If they attempt this Phabricator warns the username already exists (because it does) and reports a Duplicate error.. Phabricator is set to accept their samAccountName and this matches their existing Phabricator username. Clearly Phabricator must be using the correct samAccountName otherwise it wouldn't recognise the duplicate, but if this is the case why does it see the user as new and asks them to register. Nothing has changed in our AD nor the users.