Quantity not in shipment column calculation method

Hello, On Sales Order > Pick & Pack > Picking List Registration, if I change ‘pick quantity’ column on tab Lines, ‘Quantity not in shipment’ column On tab Order Picking Overview will be updated itself when i click the grid. Where can I see the method for ‘Quantity not in shipment’ column calculation? I put break point on Table WMSOrderTrans > method ‘insertorUpdate’ but it doesn’t hit. Thank you