Hi Magnus,

Well, the browser back button isn't broken. It's just the behavior of resubmitting the web form via standard POST...

We plan to implement the ability of the checkout process to handle such user behavior into some of the next versions.

Currently, you have an option to allow Use Update Panel for the Shopping Cart web part...(AJAX properties group)

It's easy, it will smooth your checkout process by partial postbacks, and when you hit the browser back button somewhere in the middle of the process, you will get back to the page from which you've entered the checkout process (e.g. before the shopping cart content) - no matter which step you were in before.

No expired page, no resubmission warning... all the entered values are retained.
The only disadvantage is that you have to go through the steps to get back to the one where you hit back button... So, just keep hitting the next step until you're back in the desired step :)

Hope this helps.

Regards,
Zdenek