Membership plugin bug

Team, i have two subscription plans created in membership plugin. Plan X and Plan Y

A) once user is subscribed into plan x and he paid for it throught paypal. then 5 minutes after that he pay for plan y without any issue or error message from membership plugin.

is it possible to limit plugin, so user can be registered only into one subscrption plan at time ? or it is bug ?

B) second issue is definitely a bug. once user registered and paid for plan x. He goes to his renewform [ page is called renewform.php] he just easily click on plan y and boom he has plan Y activated even without pay !!! bug ?

THank you for advice