Registering for a paid event as anonymous but with a contact's email address changes another contact with the same first name.

Running Drupal 6.15 and CiviCRM 3.0.3 with aprox 2500 individual contacts. You can not register for a Drupal account on your own – an admin needs to create the Drupal account for you.

The following happens intermittently and we have not been able to reproduce it consistently. Here are the steps that we've taken to have it happen:

1. Create a new paid event with online registration.
2. Include "New Individual" profile during registration.
3. Confirm that permissions are set so that an anonymous user can register.
4. Create 3 contacts all with same first name, different last names and unique email addresses:
John Smith1, jsmith1@domain.com
John Smith2, jsmith2@domain.com
John Smith3, jsmith3@domain.com
5. Go to the event registration page as an anonymous user.
6. Register for the event using jsmith1@domain.com, same First Name, new last name, something like "Newlast1"
7. Enter your billing information and complete registration.
8. Verify that jsmith1@domain.com has been registered for this event and that the last name has been updated to "Newlast1"

While in principle I understand that if there is a match in the email address that the info should be updated... I feel that there should really be a prompt or some info that tells the user that this info belongs to someone else and that you should enter your password to login or you should use a different email address. The contact info shouldn't just be updated. I'm not sure if this is a related? Have a look: http://issues.civicrm.org/jira/browse/CRM-5969

Having said this, what happens in our installation is that in some cases, jsmith1@domain.com is updated and the contact is registered for the event. However, what is more disconcerting, is that in other cases, when you repeat the above steps, jsmith2@domain.com or jsmith3@domain.com has been registered for the event, and their last name has been changed from "Smith2" to "Newlast1" or from "Smith3" to "Newlast1" – which is just plain wrong.

Some (somewhat) related thread that I discovered while researching this if it's useful:

• http://forum.civicrm.org/index.php?topic=12448.0
• http://forum.civicrm.org/index.php?topic=11267
• http://issues.civicrm.org/jira/browse/CRM-5538

Thanks much!