Yep, that registration process is a mess.... looks like still in beta version. It's a joomla registration, not a store registration... how many customers possibly lost by a user scary experience....
The worst is after registration, with the message "Registration complete"... It opens an empty page with the message fixed in bottom right of the page.... As the class of that message is dependent of "system-message-container", if I change the css, it will change in many places of the site....
What would have been nice is that on the previous page where you either connect or fill your infos is that if you have already an account, you click on connect and a dropdown comes with user and password to fill and that's it.