I noticed a while ago that in the Category:Warframe Abilities, not only were the abilities members but also both the Warframe_Name (Warframe) pages that cast them and their respective Warframe_Name/Abilities subpages. I only figured out today, with some explanation from User:brizingr5, that this is because when a page is transcluded, its categories get transcluded as well. As a result, the wiki believes that not only is Ember's Fireball a warframe ability, but Ember herself is a warframe ability. This is especially troublesome because, as it is not a substitution, people who wish to try to fix these erroneous categorizations will not find the offenders in the sidebar or whichever location the visual editor uses (which I don't ever use anymore). The only fix is to remove the category from the root, go to the pages transcluding the root, hit "edit" and then "publish" on each, then go up a level and remove the pages transcluding the level 1 branches, and so on until all pages are "refreshed".
The proper way to avoid creating the problem is to put categories into the source between exclusion tags:
By doing this, we keep categories tied only to the relevant page and do not let them invite in other pages. Alternatively, being very selective of your inclusions works similarly:
And of course, remember that it's a different command than the following, which totally does NOT solve our problem:
That one would just be plain wrong.
It would be difficult and unnecessary to make these changes on all existing pages, and most pages do not even get transcluded and are consequently unlikely to cause issues. But, sometimes these things are hard to predict, and if we all follow the practice of only adding categories between exclusion tags at the bottom of pages in their source, then the problem shouldn't arise again except for new authors who haven't yet learned this.