Event Registration fails for anonymous user registration

1. Make a anonymous Event Registration for unpaid Event. http://drupal.demo.civicrm.org/civicrm/event/info?reset=1&id=2
2. Once you done with registration, try again same event registration, http://drupal.demo.civicrm.org/civicrm/event/info?reset=1&id=2

You get error message:
"Oops. It looks like you are already registered for this event. If you want to change your registration, or you feel that you've gotten this message in error, please contact the site administrator."

This problem might be related to session. We might need to reset CiviCRM session once user is done with registration process.