Hi David,
In what screen do you see that address as different, the main Edit Customer screen or another screen?
Customers and Leads are actually located in the same table in Method, the Entity table. The only difference between the two is a field called IsLeadStatusOnly. For a Lead record, this field is set to True and prevents the record from syncing to QuickBooks. For a Customer, this field is set to False and the record then syncs over. As a result, when you do a Convert to Customer, none of address fields should change as its in reality the same record.
- Adam