original bug in tfs #45140
It is not obvious that you need to klick the "reload"-button on every order row in the checkout if you change the value in the quantity field. if you have many product it is very easy to miss this button and there are no validation done on these values and the cart values so there is a big risk that many will place order with wrong quantity. Also you need to press every row if you want to update the values for alla the product in the cart.
This ability was shipped as a new feature in Litium 8.0.