Sorry - I copy and pasted. I forgot about vbulletin doing the ... thing to the visible URLs.
Basically - We added an article to a category but the article didn't show up in the category page. After some inspection, we realized that if we added the category tag at the TOP of the article, it was added to the category page. If we add it at the bottom of the article, it doesn't show up in the category page.
At least that's the conclusion our wiki guys came up with.