Opt in settings

i am trying to use mailchimp to harness my woocommerce email details when a customer checks out…… For those customers who check the “opt in” checkbox at checkout… They are added to my Mailchimp “Audience” However, They are not a “Subscriber”, Under the “email marketing” column, they are shown as blank, when i click on the customers email, they are described as eligible for “Transactional emails only” I would assume as they have checked the opt in box at checkout, they would be a subscriber? Under the mail chimp settings (within wordpress), under “Audience settings”, the check box is described as follows: “Opt-in Settings – Message for the opt-in checkbox – Add text to go along with the other opt-in checkboxes. – Customers can click a box at checkout to opt in to your newsletter”. i would assume that any customer who selects the check box, is opting in to emails and would therefor be classed as a “subscriber”. is this a bug? or functioning as expected and my expectations are not correct. any help much appreciated.