A course could be displayed twice on the Report Card because there is no Teacher listed for the Term that the Course is duplicated for.

To see and fix this, navigate to:
  1. Academics > Scheduling > Requests and Schedules > Set section info
  2. Search for Course that is Duplicating
  3. Switch to other Term(s)
  4. If there is no Teacher listed, click -Not Set- and select a Teacher
This can also be done in Classes > Manage Sections.