I have a little problem with this now.
I have created the line in database and all works properly but this is what I see now.
A normal customer makes an order and all it's allright, the amount is correct... all ok. But in the back end I see product price as 0,00 even although the total is well.
In frontend checkout is correct.
Users can also change the payment method in their account and now if they change for exmple from collect on delivery to paypal payment method the product price is 0,00 so it charges only the shippment.