When changing the UOM in an orderline will not change the price field. While that's no problem if the price leaves unchanged it will usually lead into a problem if the price is changed. As example selling a sixpack instead of 'each'. The user will see the price for a single item and therefore enter the reduced price for a single item. But the calculation takes this as price for the sixpack. It's correctly mentioned in the help window that the price is based on the currently selected UOM but nobody reads this.