Hi,
Ah, I thought you were talking about the email address, not the address address.
I don't see why an empty address would be created.
I've contacted JFBConnect so that they can provide a copy of it so that we can debug the issue on our end.
Unfortunately, we were not able to reproduce the issue.
When I click on the "login with facebook" button of JFBConnect, I first get a Facebook popup so that I can accept the connection with my Facebook account. Then, I'm redirected to the JFBConnect user registration form where I need to enter the password I want and then I am redirected to the activation message page. I then click on the activation link of the email sent by JFBConnect and I can then log on the checkout with the user account created. I didn't get any blank address created by JFBConnect for that user account.