Multiple contacts sharing an email address

I tried editing a contact when I tried to assign an email address that was already used by another contact. When trying the save the contact, I got the following:

Sorry. A non-recoverable error has occurred.

DB Error: already exists

Database Error Code: Duplicate entry 'staff@example.com' for key 2, 1062

BTW: When people use the CiviEvent sign up page, they CAN register multiple people with the same email address. ( as described in http://issues.civicrm.org/jira/browse/CRM-4167 )