Production order and sales order reference appearing blank after changing warehouse dimension in production order


I am using AX 2009. I am generating production order through sales order lines. After generateion of produciton order I am chinging warehouse of that respective production order. When I changes that warehouse then Reference (of Sales Order with number) from production order is deleting and displaying blank. vice versa also even in sales lines → other tab page its showing reference of production order. I want to avoid this of deleting of reference from production order after chainging warehouse dimensions. Where to apply customization? Can any body help me?