The Registration Confirmation email uses the Registration Details template code, which summarizes the participant responses made on the registration form. 

In the past, checkbox questions would display the slug from the question response. For example, the question "Terms and Conditions' might have the slug 'terms'. When a participant agrees and checks the box, we would display the word 'terms' in the email template code. 

We have now updated the Registration Details template code so that it will display the words 'checked' when a checkbox has been checked by a participant, instead of the slug.