Modified events cannot be deleted

If one modifies one instance of a recurring event, changing the start date, and them later tries to delete that modified event, the modified event instance is still shown in the calendar.

Deletion of that instance causes a delete mark to be placed for that event, however with the old date of that event instance, and the modified event is not affected.

Workaround: delete the modified event instance from the event in the object editor (if one can find that event :-/ ). Unlikely that users will figure this out.