Many/most cards do apply the payment to the balance that is least beneficial to the customer.
Capital One does have a policy, at least when I did it end of 2016, that as long as you make the minimum payment plus the new purchases balance in full the transferred funds stay at 0%. Another nice feature they have is to lock a card to prevent it from being used to avoid any problems. I have 2 Cap1 cards and didn't want to mess up which one to use so I locked the card.