Purchasing UOM of BX vs MRP messages to order in EA

When processing MRP messages it says to order as EA even though in item master Weights & measures for purchased items we have set UOM as BX. Why doesn't MRP convert quantities to BX when you process message and generate PO? Shouldn't it convert the EA quantities to BX quantities assuming our UOM conversion is correct? Seem like I had this issue with another client and we had to do a modification to the PO print program to have it print as BX instead of EA quantity.