I've got a bit of a baffling issue and I'm not sure where to begin looking for fixes.

I have begun to notice several instances where I have several contacts that share a single Drupal user account. These are contacts who are clearly not the same person and have no business sharing a single Drupal account.

Any idea what might cause this to happen?

I've got a bit of a baffling issue and I'm not sure where to begin looking for fixes.

I have begun to notice several instances where I have several contacts that share a single Drupal user account. These are contacts who are clearly not the same person and have no business sharing a single Drupal account.

Edited to add:

• I'm using CiviCRM 4.6.8 and Drupal 7
• None of the contacts share the same email address
• Contacts are not synced via rules
• We have recently opened registrations for 2 very large events. The merge rule we're using is supposed to sync contacts on name and email address
• There is a profile used for site registrations. We collect name, email address, phone number, address, etc.

Any idea what might cause this to happen?