As editor, click on a course event in the calendar to view it, then hover over the delete button. The tooltip says "Delete event". However, if you click the delete button, you are in fact deleting the whole activity, not just its representation in the calendar.
This is a serious usability issue, which has seen our editors inadvertently deleting activities when they only wanted to remove the event from the calendar.
Calendar entries that are automatically generated by activities should not have a delete button next to them.
Activities should have an extra option: Show in calendar/Do not show in calendar. Deleting the event for such an activity would then simply toggle this setting.