Hi, i have a question about the log note in every delivery.

For example, i have a sale order with product P quantity 10, price unit 12000. I add a shipping with method base on rule (whenever the price < 500000 then 10000*quantity). I confirm the sale order then i have my first delivery order. 

I click on validate button on delivery with quantity of 6 marked as done to create backorder. And then confirm the backorder as well, both the log note of the two delivery order show the shipping cost of 10000 $, why it not show the shipping cost like 60000 for the first delivery, and 40000 for the second delivery ( i taught it calculated base on the delivery not on the sale order). You can see the images below.