Here https://fr.wikipedia.org/w/index.php?title=Henri_D%C3%A8s&diff=105153393&oldid=104979477 and here https://fr.wikipedia.org/w/index.php?title=Henri_D%C3%A8s&diff=next&oldid=105153476 the categories are gone as well. (Wasn't that impossible to do, as per bug 61858?)

(To clarify, obviously categories can be removed from an article anytime, but from the diffs it looks like the user has selected and deleted a huge part of text at the bottom of the article, and it doesn't seem that he was there to vandalize it - hence, could be a bug.)

Maybe this was invalid. There is a "Sort this page by default as" option in the Categories section of the settings dialog, so now it's pretty obvious how one can change or remove that option, but I don't know when this was introduced.