WooCommerce Bookings

I consider this one a bug that needs to be fixed;
http://mojofit.com.au/product/pt-session-30-45-minutes/

You can book the same session twice!
Make a booking, it gets added to your cart.
But then you could add another booking for the same time slot and add it to the cart.

The flow chart needs to be different because if you book a session and checkout, you couldn’t book the same time slot again because its booked out.

But the fact that you can book it twice while you are on the product page needs to be fixed.