Shipping Address Refuses to Change in Checkout

[korak]

This problem occurs for registered users:

Once the user ships to one country and then wishes in the next session to change the shipping address to another country, the cart responds by not letting the user check out. Instead the message on the Check Out page displays "Ship to address has changed. Please return to cart" - even if the new shipping zip and country were previously entered in the Shipping area of the View Cart page.

We are using v. 8.0 and do not wish to upgrade to v. 8.1 until bugs like this one have been resolved:
http://support.shopsite.com/forums/view ... ry+changed

Thanks for any ideas on this. Bug has been replicated in three different browsers, including IE 6 on Windows XP, Firefox 1.0 on OSX, and Safari on OSX.