Product Qty Maximum only allow half of quantity to added in shopping cart page

[HeyIts007]

Actually it works fine if I type in the 2 or max qty at the first time I add to cart, but it gives the error if I start with 1 in the cart and then modify the cart to 2 or max qty.

reference module;
/includes/classes/shopping_cart.php

i.e. I presume it's line 1560

if (($new_qty + $cart_qty > $add_max) and $add_max != 0)

This seems buggy