PO20 Replace Item Unit of Measure Error

I was looking for a patch for a unit of measure error my buyers are receiving when they replace a item with another item number that does not have the same unit of measure as the original item on the requisition. What I found was a article on the knowledge base (article # 5367593) saying that this is a valid message.Now I am trying to understand why Lawson would want PO20 to act in such a fashion. I do not care what unit of measure was on the original requisition I just want to maintain the link from requisition to purchase order.Lawson's solution was to delete the source or add the unit measure. Anybody have any ideas on why Lawson has PO20 checking the unit of measure on the purchase order line back to the original item on the requisition after the buyer has replaced the item.:confused: