Multiple sign-ups from single paypal account

I’ve searched through the forums (and elsewhere) but I haven’t been able to find an answer (maybe I am just using a poor choice of words in my search). This is the issue we are currently dealing with on our site.

Person A purchases a membership for themselves through paypal. The money is accepted and they are redirected to the site to create their account. They then decide to create an account for Person B. They have not logged out but they go through the process, paypal accepts the payment, but then nothing happens. They don’t return to the site to create an account (because they are logged in) nor is it applied to their account. The money is just swallowed up.

Is there any way to prevent this from happening?

As a side note, I have had members claim that this situation also happens when they aren’t logged in, but that is usually relying on their memory. I know it does happen when they are logged in for sure.

It doesn’t likely matter to this, but this is what is currently installed.
Wordpress 3.6
s2member Version 130802 + s2Member® Pro v130802