New Version removes members old subscriptions when subscribing to a new one

I have my site setup using membership to allow access to specific access levels by using shortcodes. On the new versions of membership, when a member subscribes to another subscription plan, they are automatically removed from one they already have, forcing me to go back and manually add everything they already had access to before getting the new subscription. I am having to use version 3.4.6.1 to avoid all issues that existed in the versions leading to the new one.