Returning Guest checkout blocked.

-- HikaShop version -- : 2.5.0
-- Joomla version -- : 3.5.1
-- PHP version -- : 5.6
-- Browser(s) name and version -- : All
-- Error-message(debug-mod must be tuned on) -- : Standard System Message: Email address already used

Hika Checkout config:
Login: No
Registration: Guest

Our site doesn't have user registration at all. (In the past, the user registration checkout was entirely too confusing for our user base). We use guest registration. The relevant config settings are attached in several screenshots.

From the config, it looks like we're using pure guest checkout; however, when users return and attempt a 2nd guest checkout, they're stopped with the standard system message "Email address already used".

Can you confirm my config? Is this expected behavior?

Checkout Workflow Config

None of the problem emails are in the joomla users table (#__users) - we only have three site user accts, and all are controlled. There ARE thousands in the hika users table (#__hikashop_user), though. Are these Hika users safe to scrub out without breaking anything?

The users are definitely in the #__hikashop_user table (we have several thousand hika users, but only 3 joomla users). These #__hikashop_user entries are safe to delete?

Hello,
Note that you will get a "Email address already used" error message only if one of your Hikashop user account (guest email address from the #__hikashop_user table) is linked to a Joomla user account (from the joomla user table)

These #__hikashop_user entries are safe to delete?

Hi, I had the same issue today even with the latest version of HikaShop, and having removed all joomla registered users from the #__users table, the user that was having trouble returning with the guest checkout had previously a joomla registered account, which i removed when i converted to the Guest Checkout, as per your instructions for setting up a Guest Checkout, But in the #__hikashop_user table the field user_cms_id was set to that users old Joomla registered account id, setting this to zero solved the problem. Hope this helps someone else.