Displaying an activity's description field based on group settings does not work correctly

Reproduce:

1. Add a group called e.g. "Students"
2. Add an Assignment with a description and tick the check box "Show description in course"
3. Configure the assignment so that it should NOT be displayed for the "Students" group.
4. Log in as a user of the "Students" group.

What happens: Moodle will display the assignment's description in the course for the users of the "Students" group.

Expected: The description of the assignment should not be displayed for the users of the "Students" group.

Seems to be a problem also for other activities.