Oh geez. My client has about 5 lists, and each person can perceivable be on all those lists.
And the web forms I built to integrate with Constant Contact, focus on one of these lists. So if a user fills out a form, such as "volunteer" instead of "contact us" not only do they get removed from the other lists, their answers also get deleted from the constant contact database, which would more than likely still be accurate.
All of their lists share the same contact and custom fields up at Constant Contact.
To clarify the other issue - I have noticed that if I leave a field empty on one of my forms, such as "Street Address 1" - if data was already in that field at Constant Contact, and I submit my form with that field blank, it will then erase the field up at Constant Contact - when it should just leave it as it was.
I hope there are future options not to change other lists, and not to change or delete fields in constant contact, that are not filled out (null/empty) on the new form being submitted. It should just leave the existing field there.