Hidden activity and gradebook item

Step to reproduce:
1. Add hidden activity test1.
2. Visit Grader report.
Expected result: hidden gradebook item test1 (may be gradebook must not have such item).

At this moment I must go into gradebook and manually hide such item. Another unnecessary and strange step.

Another problem: I hide activity. But gradebook item doesn't been hidding. Why? I don't understand logics in those cases.

I see mdl-8850 and mdl-12270. I can understand logic why hidding gradebook item not hide course element. But can't understand logic in opposite case.