I've just checked, and although the code responsible has been restructured a bit, the sort order is still the same.
And it is working for me. Let me explain how it should work:
There is a sort-order field in the database
, so you can order things manually. However, if all the sort-orders are the same, then it will sort alphabetically. And new categories are always created with sortorder = 999.
So, if you want to get back to alphabetical order, then you need to execute some SQL
UPDATE mdl_question_categories SET sortorder = 999 WHERE context
or WHERE parent = XXX. You need to find an appropriate XXX by looking in the database. This assumes you are happy fiddling around in the database.