Second List + Existing User + New Fields = No update

Hey, I’ve got the following problem:

On my site there ist a simple form for newsletter subscription (company, name, mail) -> List 1.

Now I’ve created a new form for another subscription (company, name, mail + street, postcode, city) -> List 2.

If a new user, who didn’t subscribed yet, subscribes, everything is fine. If a user who already subscribed for List 1 subscibes from the second form, the additional fields (street, postcode, city) are not updated (blank).

It would be nice if already registered users could enter themselves in the second form and the new fields would be adopted.

Is there a solution?