I came across an issue today regarding the hosted order forms. When someone fills their billing information and chooses paypal to checkout all the fields are overwritten by the data received from Paypal.
So for a user having paypal account on a different email it creates a different user inside infusionsoft causing more confusion for the user. If someone sees it they can update the email address but in most cases everyone just clicks on the complete purchase button.
Tested it on a basic order form theme as well.