I don't think there's inherently a bug here. Admittedly these are a little awkward to touch accurately with your finger (we do hide them on narrower screens), but in my testing with iOS 9 it is possible to touch them. Unfortunately if you miss, it will activate our "touch proxy" system, which is where you can tap on any where within the thread list item and it will proxy that tap through to the thread title link, which will therefore navigate to the first page of the thread.
I suspect the only problem here is you "missed" the page number.
It does make me wonder if we should just start hiding them on touch devices entirely, but that potentially hides them to users who use hybrid devices with both touch and traditional inputs.