Board Thread:The Drax Cave/@comment-7302713-20130424002107/@comment-188432-20130425131328

already adds all the categories that are necessary to the article. We have taken to adding category:years to year articles simply because the year pages are currently involved in the Game of Rassilon. When that track is disabled, category:years will be pulled from all the year pages.

What you're describing isn't really a bug, though it's sort of "technically interesting". See, adds all the categories automatically. Therefore, there are no categories directly on the page. When you add category:years, it's the only "natural" category on the page. For that moment it therefore appears to clear out the page. But if you simply reload the page, you'll see everything pops back to normal.

The "xth century years" and decade categories should never be added manually. It is correct that these categories should not appear in the category module in the editing window. If you ever see these categories while editing a year page, you should manually delete them. They must only be on the page as a consequence of using the template.

You should simply get in the habit of reloading the page after using the category module. It has other "technically interesting" features that do not resolve themselves until after a page load.