This is really a bug, not a feature request. When you reach the checkout, the associated account is retained in local browser state from a previous log-in. However, even you access the account page and explicitly log-out, the checkout still retains the account. Furthermore, it is not possible to change the account you are using for checkout. This would be very bad for any user that accesses the site from a public computer. A completely new user who has gone through checkout... but has never logged in before (as their account was just created and presumably a random password was generated) is treated as logged in. Again... very bad if you are on a public computer. This info should only be retained after an explicit login.