You have to commit the item to a different order before setting this order back to Available Quantity. Example: Let's say I have an order for 100 widgets, I have 100 widgets available, and the order has all 100 committed. Now, I get an order from a priority customer for 10 widgets. So I change the order line of the first order to Do Not Commit and submit. Then change the second order to Available Quantity and let it recalc when you save the line (recObj.commitLineItem('item', false);) . THEN go back to the first order and change its item line back to Available Quantity. Result: first order has 90 committed 10 back ordered and second order has 10 committed.