Dropped/Withdrawn students listed as “Managers” in the Discussion Board

Problem: Instructors visiting the “Manage” area of their discussion board may see students who are listed as “Managers,” yet are not in the course.  This can happen when a student enrolls in a course (however briefly), and subsequently drops or withdraws.  Despite their being listed as a manager in the discussion board, they do not have any access to the course, and they are not listed as a manager if they re-add the course.  There is currently no workaround or fix available for this issue.