There is a bug in the cart process that allows users to go through the cart without checking the captcha.
There is a message that tells users "Notice Please check the captcha" on the following page, but it's easy to miss and really users should not be able to get to that page without filling in the captcha.
It allows users to finish their order BUT DOES NOT register them as a user.
It can be tested on a fresh clean install at http://vm.testcms.co.uk/index.php/vm/test-detail
Thanks