how "pinned" works?

I was in process of starting to build out my talkyard. I have a category of "SOFTWARE" with a sub-category of "LaundryLog"

I created several topics, each of which happens to have been made a wiki as well. I set the "LaundryLog — Start Here: What It Is and Why I Built It" as pinned. So I was surprised when I went to the category and the "pinned" topic was at the bottom.

Is my expectation that a pinned topic should be listed first incorrect or is this a bug or is my understanding of a pinned topic incorrect?