Hi,
I've never seen that. It should not have any address in the checkout since the fields of joomla are not compatible with HikaShop's address system.
Instead of the joomla registration form, you should use the hikashop registration form (menu item of the type hikashop user registration form). That way, the address entered during the registration will be in the checkout automatically.
For that problem in particular, that would happen if you had imported the data from a previous website with the user ids being different in joomla. Which would mean that the previous addresses of users would be assigned to user ids who don't exist and upon creating a new user, the new user id and the user id referenced in the address table would match.
That's just a supposition so hard to say what to do. Could you confirm or explain what you did ? Where these addresses there before ? Did you add them in some way ? An import ? A migration ?