Hi. If a user first buys a subscription, they are redirected to the purchase page for the specific membership button that they push. If they are already a member of one subscription and they choose to select another subscription, they are taken to the subscription page instead of the specific purchase page for the membership button that they pushed.
The behavior should be consistent to avoid confusion. When a user thinks they have selected the item they want to purchase, they should not be offered a choice again.