The user picker doesn't display correctly the users that were previously selected from other wikis

Follow this steps to reproduce:

• on a subwiki that supports both local and global users
• edit a new page with the object editor
• add a rights object; the user/group picker must have the scope toggle
• select a global user and choose whatever right you want
• save and edit again

The selected global user is not displayed correctly because the user picker looks in the local wiki by default (the scope toggle is set to local by default).