Multiple subscriptions: impossible with latest version?

I just updated from version (purchased in 2013) to the latest
To my surprise users cannot buy more than one subscription.
I went back to and found out that users can again buy one or more subscriptions, using the same account.
Have I done something wrong?
Is there a setting somewhere that needs adjusting?
And one more question: is there a page where a user can view the subscriptions he/she has already paid for?
Thank you.