(Option price) ERROR?

Hi!

I have been using your wonderful plugin for a long time, but I have a problem.

When I select an option with cost it is correctly added to the total if I only buy one unit of the product.

But when I buy more than one unit of the product, the cost of the option is not added to the total.

How can I solve that? Is it an error or can it be solved by buying the PRO version?

Thanks