I don't know if the magento developers see this post, but supee 10570 has a bug. I already added my message in the bug report section.
In magento 1.8.0 the guest creation at the checkout will result in a redirect to the front page, so no success page after the checkout.
A temporary solution is to enable e-mail confirmation on account creation. I found this solution here:https://magento.stackexchange.com/questions/215292/security-patch-supee-10570-possible-issuesI saw that there would be a new patch version for 1.7, will there also be a new version for 1.8?