Thanks for your response.
I understand the limitations of limiting to the current parent - children. But sometimes that would be desirable or maybe if the cats were sorted with current and children at the top, that would suffice.
Apart from that, the main problem is that several times I have replied as linked topic, without setting the category and it places it in uncategorized - even though this option is unchecked in admin. The user wouldn’t be aware of that or where to find it if they did that.
Perhaps being allowed to not set a category when Admin > allow uncategorized topics is false, is a bug? Or maybe I’m doing something wrong.