Single tag is assigned multiple times to the same contact

When 2 contacts are merged which happen to have the same tag(s), if the user chooses to "move tags" during the merge then the database table civicrm_entity_tag ends up in an invalid state.

To check if the database table is in an invalid state, run the SQL statement:

SELECT entity_id, tag_id FROM `civicrm_entity_tag` group by entity_id, tag_id
having count > 1
order by tag_id

If this query returns anything, then this means the table civicrm_entity_tag has invalid records, and the upgrade script to to go CiviCRM 3.4.5 will fail.

This issue affects the upgrade script is described at: http://issues.civicrm.org/jira/browse/CRM-8611