Ok, this is not intuitive at all. If you add someone as a follower and would like to upgrade them to an editor and maybe some other type of user. You need to send another invitation (unlike changing an editor to administrator which you can just edit) and they will automatically be changed to an editor in the 'all users' list. This happens if they have accepted the invitation or not. Why not let the administrator just change their role without the additional email? Now if the user has not accepted or even looked at the first email they will get a second email.