Update Free Stock quantity when writing off stock

A customer has noticed that the 'Free stock quantity' is now static when writing off stock. It brings through the current Free stock when you enter the Stock Item Code and Warehouse but doesn't update when you enter the amount you want to write off; in previous versions the Free stock quantity would update to what it would be after you save the write off, and when writing off large amounts of stock over several codes this made the process much quicker. I'd recommend either having the Free stock quantity dynamically update, or add a 'New Free stock quantity' field.