Grades for courses, that were repeated in other semesters, count twice for statistics

[DrPatStar]

When failing a course in e.g. summer semester 2015 and then selecting the course again in summer semester 2016 but it has a slightly different name, and passing, the new grade is counted twice (once for each course) in the statistics. (Example: Algorithmen und Datenstrukturen 1 & Algorithmen und Datenstrukturen 1 (für InformatikerInnen)