limited stock - unlimited qty addable to cart

[supermac]

I've 50 product's units in stock but an user is able to add 1000 and more product's units to cart in this way:
1- he add 49 product to cart
2- he add further 49 product to cart
3- again and again and again and ...

The add-to-cart process checks product availability counting "product's stock minus ordered items" so if customer try to add 51 units to cart it reports an alert and limits the added quantity to available quantity, but available quantity it doesn't consider the item already inserted in cart... this allows customers to bypass any control on stock limitations!

[supermac]

I seen in components/com_virtuemart/helpers/cart.php is a TODO....