When I in course with enabled outcome usage go to add new assignment moodle allow me to select "New category" in "Common module settings" for "Grade category". It is very good feature.

Grade categories can be nested and it is too very good feature.

But when I try to use base categories in my course i must after each adding of new assignments remember to go to category editor and manually move automatically added assignment's grade category into appropriate parent category.

I think that the feature to add new grade category for new assignment must be separated (into checkbox) from list of categories to select parent for assignment's grades. And when check box "Add new grade category for this assignment's grades' will be checked by user, new category must be created in category, which selected in "Grade category" listbox.