Unit price adjusted by shippable quantity in the update mode

i face a critical case

when entering sales order and order quantity was partial available and modifying business unit header or anything else, unit price adjusted by stoppable quantity.

for example:

in add mode

Quantity order = 100

Quantity back-order =75

Quantity Shipped = 25

Unit Price = 20

in update mode:

unit price changed to be = ( Unit Price / Order Quantity ) * Shipped quantity = 20/100*25= 5.