cakephp why can't I have an admin route and a superuser route?

In core.php I can define

Configure::write('Routing.admin', 'admin');

and /admin/controller/index will work.

but if I define both

Configure::write('Routing.admin', 'admin');
Configure::write('Routing.superuser', 'superuser');

and try to look at /superuser/blah/index/ instead of it saying the controller doesn't exist it says

Error: SuperuserController could not be found.

instead of saying

Error: BlahController could not be found.

When I first read the documentation I was under the impression I could run both routes, and not just one or the other. Is there something more I need to do?