I believe this may be a bug. I am using version 1.1.9 with the default_html5 template. And I have tested this in FF, Chrome and IE to see if made a difference, it did not.
Steps to replicate the issue: Place an order as Guest and complete the order is at index.php?rt=checkout/guest_step_3 , choose Edit Cart
This returns to index.php?rt=checkout/cart
if one edits the shopping cart and fails to click on the update button (I know it is needed, but folks do miss it) but instead clicks on the Checkout button it returns to the account login page. index.php?rt=account/login
Customer does one of several things, but all fail: they re-input the guest info, and it won't recognize the checkout correctly, each click goes back to the account login.
or if they use a page-back on the browser the order is still there, but continues to fail rather you use the update or the checkout button. There is no easy solution for the Guest to complete their order.
This behavior doesn't not happen if one has a registered account, only in the guest checkout.
The current resolution is to disallow Guest option - but would like to have it available.
Thanks
Lee