Problem with partner product reference and code

On a product form, tab 'Prices & Suppliers', you can define another product name and code for each supplier. Then, when you make a purchase order to this supplier with this product, it will show the partner product name and code on the purchase order, in place of the internal product name and code. This is working correctly when we make a manual new purchase order BUT not when the system create an automatic purchase order.
For example, if I define a product as "Make to Order" and "Buy" to supplier "Distri PC", with a new partner product name and code, then when I make a sales order for a customer with this product and validate it, I will get a purchase order in "Request for quotation" state. On this PO, the product on the PO line will show the internal product name and code instead of the partner product name and code...Now, if I open the PO line, remove the product and re-enter it, it will take the partner product name and code correctly.