I have a custom module (Multiple Flat Rate Shipping (magento.com)) that add multiple flat rates and make me able to show different prices for different zip codes.
In the cart everything works, but in the checkout page I have to compile with shipment data the form and reload the page (not www.domain.com/checkout/#shipping bcs it keeps loading forever but only www.domain.com/checkout/).
After the reload I can change the zip code and it works. The XHR request on the first page load is half empty with some dummy data, and when I reload the page it sends the actual data that I have entered.
