It seems that existing Blueprints that are based on a certain C++ class don’t update properly when you change that class’ [FONT=Courier New]UCLASS() annotation.
For example, I had created a Blueprint based on my class so I had something to work with, then I tried to customize it to work the way I wanted in the editor. But when it came to hiding categories, the changes were never picked up because the Blueprint had already been created, so the damage was done, so to speak. Once I deleted my Blueprint and made a new one based on the exact same class, all the categories I had hidden were gone. This works fine for me now:
Also, I don’t know if my fix is related to TiGuy’s problem; I just tried hiding Transform as well, and that didn’t seem to work, so maybe it needs to be there? My class will be [FONT=Courier New]notPlaceable so I won’t have to worry about the details view much, but I did want the Defaults view in the Blueprint editor to be clean.