Role subscsriber deleted for Customer

Hey,

I’ve got a problem : on my website, I’ve got 250 subscribers. When a subscriber books his first session, this subscriber becomes “Customer” and Subscriber role is deleted.
And because subscriber role is deleted, they have access to back end…

I had to switch every body in customer and add to every one the role “subscriber”, then they’re not redirected to back end. I also have to hide admin-bar for customer…