It seems to be a common misconception that the STD pricelist field you set in a product has an effect on ordering.
IT DOES NOT
Because a product can belong to multiple pricelists, the Std Pricelist selected on a product is not the best selection criteria for orders.
The Std Pricelist selected on a product will update information about the product such as the standard cost and other details, eg RRP, PLU,... when a 'Pricelist Update' is run for the Pricelist set in the standard Pricelist field.
If a pricelist (or pricelists) is selected on your order type criteria, then products ON (belong to) that pricelist will be selected for the order. If an item is NOT ON that pricelist, it will not be selected for that order.