"same email address?" in event overwrites contact name

Originally found in CiviCRM 4.1.2

Contact name is overwritten with guest's name when;

• Both "Register multiple participants?" and "Allow multiple registrations from the same email address?" are both enabled, and
• The guest shares same email address as well as last name.

Steps to Repro:

1. Create a test account with full name and email. (Example: Mr. Contact1 Test, test@gmail.com)
2. Create a test event. Enable Online Registration, and tick both boxes for multiple participants and same email address. For the Profile for Additional Participants, collect at least full name and email.
3. Test-drive registration as the contact you created in step 1. Register 2 participants, and the second person should share the same email address and last name as contact1. (Ms. Contact2 Test, test@gmail.com)
4. Complete registration. Check contact page of Mr. Test. It is changed to Ms.Contact2 Test. Also, when you check event participants list, there are two entries for Contact2. Screenshots attached.

I could reproduce this on my local 4.6.5. and 4.6.7 demo site (http://d46.demo.civicrm.org/civicrm/dashboard)