User Creation via profile fails with DB Error

In WordPress and CiviCRM 4.6.0 when using a profile with Account Creation Required (via shortcode), WordPress Account is Created, however CiviCRM contact is not created.

Debug shows:

DB Error: already exists
Error Details
Database Error Code: Duplicate entry 'test@bcellc.cc-1' for key 'UI_uf_name_domain_id', 1062
Additional Details:
Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -5
[message] => DB Error: already exists
[mode] => 16
[debug_info] => INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALUES ( 1 , 6 , 'test@bcellc.cc' , 207 ) [nativecode=1062 ** Duplicate entry 'test@bcellc.cc-1' for key 'UI_uf_name_domain_id']
[type] => DB_Error
[user_info] => INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALUES ( 1 , 6 , 'test@bcellc.cc' , 207 ) [nativecode=1062 ** Duplicate entry 'test@bcellc.cc-1' for key 'UI_uf_name_domain_id']
[to_string] => [db_error: message="DB Error: already exists" code=-5 mode=callback callback=CRM_Core_Error::handle prefix="" info="INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALUES ( 1 , 6 , 'test@bcellc.cc' , 207 ) [nativecode=1062 ** Duplicate entry 'test@bcellc.cc-1' for key 'UI_uf_name_domain_id']"]
)
---------

Cannot reproduce on http://wp46.demo.civicrm.org/ as we need to do this in create mode when not logged in. We'd need content created to do this.

I am not sure where this is failing only that it fails after the WP user is created and before or when the CiviCRM contact is created.