(Planning) I returned a task from Planning back to Planning and it still has calendar information

I pressed Shift + ← to return it, but when I looked at it in the Inbox list (and also in the + Task popup), it showed the date and time information that came with it when it was recorded on the calendar!

So I had to press the Delete Only on Calendar button in the Task popup one more time to get rid of it! I wonder if I'm doing something wrong?