I agree it is an unfortunate name. It used to mean just what the name implies, a random order; but at some point someone realized that because it doesn’t sort its list, the list gets left in the order in which it was discovered–which is a depth-first scene graph traversal order–and since it turns out this is a useful feature, we left it that way and defined it as its official behavior.
Since the fixed bin uses the stable_sort() function to sort its list, it will also leave things of the same draw order in scene graph order.
Might be a handy feature, but it sounds hard and possibly expensive to implement a complicated sorting algorithm like this. Not sure it’s worth it. 
David