title: Magento. Quantity in checkout shopping cart doesn't work properly
body: <p>I have installed Magento 1.8.0 and on localhost the cart is working correctly.
  I change the quantity of a product in the cart then I push the "Update cart" button and all works fine. 
  I trasferred the site online and the cart quantity doesn't work anymore.
  As I change the quantity of a product and click the button the quantity remains the same. If I go back and try to add the same product to the cart, even if I specify a different quantity like 10 and not 1, in the cart only 1 item is added every time I click on "add to the cart" button and not 10 as specified.
  I cannot figure out where's the problem. I excluded my custom theme and rolled back to the default theme and the problem persist.
  I updated magento to 1.8.1 and the same problem.</p>