They were doing it for you because you didn't know about that button. But now that you do, they will stop doing it.

Because the past button doesn't actually do that. lol

Edit: Oops. I didn't see there are two "past" buttons. I guess one of them does do that. TIL.

Well, it's certainly handy when using a mobile client that doesn't have a "Past" button, like Materialistic :)