When using 1:1 relations, it is very important to check whether the user has actually placed a field of the linked table. You can do this by using the wildcard option with LlPrintIsFieldUsed(). If you want to check whether a field of the 1:1 linked table Orders inside the table OrderDetails is being used, you can call
LlPrintIsFieldUsed(hJob, "OrderDetails.OrderID@Orders.OrderID*");
If the result is 0, no field of the table orders is being used and it is not necessary to update the values.