When testing membership access is granted to content if payment is not completed

Hi
I am setting up a membership site and I am testing the membership levels I created a $20.00 membership and went through the steps and registered but I stopped once I got to paypal then I went back to my site and logged in and I was able to access the memberships content

is this possible this is happening because I have the payment gateway set to sandbox or is it just a bug know one has found?

In my thinking one should choose the membership go pay then come back and register using the email address from paypal or payza or in my case when they logged in they would be presented with button to complete their subscription

thanks
steve