Force page to redirect to checkout_payment if the contents of shopping cart modified

[xav2]

before customer click on "confirm" button from checkout_confirmation page,
if he doesn't quit this window, but open a new window to go back to shopping_cart, and modify the contents of shopping cart,
then closes the shopping_cart page, and click on that "confirm" button from the prior checkout_confirmation page,
the order would be placed successfully, and the costomer wouldn't check the new cart contents on checkout_confirm page.

what do i force the checkout_confirm page to redirect to checkout_payment page if the contents of shopping cart modified after customer accessing checkout_confirm page?

[mc12345678]

before customer click on "confirm" button from checkout_confirmation page,
if he doesn't quit this window, but open a new window to go back to shopping_cart, and modify the contents of shopping cart,
then closes the shopping_cart page, and click on that "confirm" button from the prior checkout_confirmation page,
the order would be placed successfully, and the costomer wouldn't check the new cart contents on checkout_confirm page.

what do i force the checkout_confirm page to redirect to checkout_payment page if the contents of shopping cart modified after customer accessing checkout_confirm page?

So, I'm curious, does this mean that if they were to go "back" and modify the cart to add more items, when they select confirm that they are given the new items at say no cost or something? Or is it just that they are then charged for the change(s) they made, but are possibly not made aware of it without stepping through the checkout process again?

[xav2]

nothing wrong, just some customers are not made aware that they add duplicate products
so it's not too important i guess