The customer reference field is a sales order header property and we cannot make changes to this field at line level, this is the feature limitation. As a result the customer reference number on the sales order line is changed to the header “customer reference” value after the mode of delivery is changed on the header, for direct delivery sales orders. The idea is to allow to make changes to customer reference field at sales order line level. Then each of the sales order line can have different customer reference value.