Ok, thanks. That explains it. Thank you for a quick reply.
However, I must admit this is very confusing for a user, it is very “implicit behaviour”. How should a new user know that these topics are special?
Coming from other systems it feels much more natural that the category description should be a property of the category itself, not being fetched from one (of many) topics. Why would there not be possible to have a category with no child elements? That is like nothing I have encountered before.
Oh well. Thanks again.