Order amount is not saved in payment record

Repeatable: Always
Steps to repeat:
1. Download Module Commerce Robokassa
2. Un-compress commerce_robokassa-7.x-1.0-rc1.zip into modules folder
3. Visit admin/modules page and switch on Commerce Robokassa module
4. Configure it (you will need an account at roboxchange.com) and buy any product

Expected Results:
Order is completed. It has related payment with order amount

Actual Results:
While viewing an order you will see 0,00 in payment amount (or order ballance) at admin/commerce/orders/{order id}/payment. Payment state is 'success', order is really payed. You can see received money in your Robokassa account. System log says 'Order #{order id} paid successfully'