Check for multiple event registrations for a contact not working

Described here: http://forum.civicrm.org/index.php/topic,6211.0.html

Lobo believes, and I was able to replicate on the CiviCRM demo with the dummy processor, that someone, anonymously, is able to register for an event twice with same email address. The person gets charged as many times as they try to register and the already existing participant record just gets changed (if different).

the proper behavior is for CiviEvent and the online registration form to prevent multiple registrations for authenticated and anonymous users with a "oops, i'm sorry..." message.

Please let me know if you need any more info.

Thank you!
Tony