Customers recieve 'Text Only' confirmation, admin's HTML

I have modified my HTML order confirmation emails to display some extra fields.

However, customers continue to receive only 'text email confirmations' not HTML.

I set the 'Admin Email format to HTML' and these emails come across displaying all the fields I added (in order.php)

However, these fields don't display correctly in 'text-only' email that goes to the customer?

Have these customers chosen HTML as their preferred email format, and are their email programs configured to display HTML ?

What is your setting in configuration/e-mail options/use MIME HTML when sending emails?

v1.3.9h Fast and Easy Checkout
My order confirmation email is plain text with these Email settings:

E-Mail Transport Method PHP
E-Mail Linefeeds LF
Use MIME HTML When Sending Emails true
Send E-Mails true
Email Archiving Active? false
E-Mail Friendly-Errors false
Emails must send from known domain? Yes
Email Admin Format? HTML

Customer Details:
Customer Default Email Preference 1

What setting am I missing? Help!