Hi,
In HikaShop, each address is linked to a user.
If the user logs in during the checkout, the addresses linked to his user account will display automatically so that he doesn't have to enter it again.
So what you're describing indicates that JFBConnect would have login the customer with an existing user account instead of creating a new user account for him.
It could also be that the user account for that address had been deleted via the database and the corresponding address not deleted, still pointing to a non existing user account, and when JFBConnect created the user account for that person it ended up with the same id as that previous user account and thus he had that address.