Sales: Committed/Reversed item quantities can't be sold

At the moment we do an 'order' in MYOB until we receive all the stock then turn it into an 'Invoice' in MYOB. The trouble with that is that if another customer places an order for the same item (that is in stock), the system still thinks we can sell it as its not reserved for the first purchase order. You then receive items for the first order only to discover you have sold the items you originally had in stock, and need to order more to be able to invoice. Which in turn delays the order even more.