The Class tab is tied to the Business Rule regarding reflecting scheduling changes. This association was made so that if a user is trying to work with All Terms and  not reflecting scheduling changes, it becomes confusing since it would show different classes in each term (and thus the other views would be better in this instance).  
  1. Select Configuration, Business Rules, Scheduling
  2. Mark the Reflect Student Schedules Changes box
OR

Select List View or Schedule View from the View menu in Enter Course Requests by Student.