Unauthenticated/anonymous users can register for events even when Drupal permissions should stop them

I require those registering for an event to have a Drupal account and be authenticated.

I have tried to force users to log-in for registration by disabling the Drupal permission "CiviEvent: register for events" for the anonymous role... However anonymous users can still register for events!
Attached is an image proving that I have played with this.

I've cleared all the caches, so it is not a caching issue.

In the profile for the "Your Registration Info" CiviEvent form I also tried setting "Drupal user account registration option?" to "required" and this also seems to have no effect.

I have been testing while logged out, of course.

I am running Drupal 7.24 in a clean CentOS 6 development environment.

TLDR: unauthenticated users are able to register for events regardless of whether permissions require authentication to register!