supplier catalog pricing not defaulting to purchase order

I have 2 items set up in supplier catalog for the same supplier, with different prices based on different quantity breaks. When entering a purchase order the pricing for the various quantity breaks pulls through to the purchase order correctly for one of the items, and for the other it does not. There are no pricing rules attached to either item, and the purchasing price level is 1 for both items. Why would this work on one item and not the other - I can see no difference in the set up of each item?