Creation of purchase info record from PO and update indicator

Dear All,

I would like the system to create Puchasing info records from the purchase order item data.
But, every time I check the "udpate info record" indicator in the PO Item, the value "X" is deleted when I save the Purchase order, and when I go back to ME23N, it has been save as blank and no infor record have been created.

Do you have an idea abiut whta I need to check ?

Thank for kind help

regards