True, it only happens with the thumbnails, but if someone posts 3 pics to create a short 3 part story-like dio segment or triptych, it appear they have posted 3 of a kind.

Well, in the sense that drawing 3 Ace of Clubs is considered 3 of a kind.

At least it works when you click the actual images. You can avoid this by opening a picture and then navigating through every pic until you get to the last one you had seen previously...but that can be tedious.