I have run into a problem where someone created a Webform using Webform_CiviCRM and for some reason added two address field sets to the contact, with the street address in one of them and the city/state/zip in the other. Now the contacts in CiviCRM have two incomplete addresses, both of the type 'Home'. When I try to export them, I'm just getting one of the incomplete addresses.
This old forum thread seems to be related. It looks like the UI on the main contact page prevents creation of multiple addresses of the same type, but the API must still not enforce?
Anyone have a suggestion for how to tackle this and get the addresses merged/squashed into a single address?