When a packing slip is posted for a non-stocked service item on a sales order line where "Prevent partial delivery" is enabled, you cannot subsequently reverse the posted packing slip quantity. Because the posted quantity is locked by "Prevent partial delivery, users are unable to make corrections or reverse quantities. However, some business scenarios require packing slips to be reversed. The only workaround is to disable the "Prevent partial delivery" parameter, which is not a feasible option considering business requirements. Hence, there should be an acceptable way to reverse the packing slip quantity, while also having the "Prevent partial delivery" enabled.