I’m not entirely sure whether this counts as a bug, but Gerke Preussner advised me to file a bug report here, so here we are.
I made a custom class that extended AActor in C++, then compiled and booted up the editor. I created a new Blueprint based off of the class that I’d just made and went to check out its defaults in the Blueprint editor. It was way too cluttered for my liking (I was only really interested in being able to alter the values I intended to define in my class later,) so I went ahead and edited the CLASS() annotation to this:
CLASS(hidecategories=(Rendering,Replication,Input,Actor))
The problem is that when I compiled my class and opened up the Blueprint that I had created earlier, the categories were still visible. I spent quite a few hours trying to get rid of them until I finally thought of deleting the Blueprint and making a new one, and that worked.
Again, I’m not 100% sure whether this is intended behaviour or a bug, but either way, it’s definitely not intuitive!