When changing the address for an order inside the UI, it locks the address so future marketplace syncs will not change it back to the marketplace value. But, when changing the address via the API, there is no way to lock it. So, changes will be overwritten on the next marketplace sync. Very frustrating and makes exposing address fields via the API almost like a red herring.
This seems like a major oversight as I imagine many using ShipStation have at least an Amazon marketplace they sync with, if not multiple marketplaces. And often little things need to be fixed or standardized from what a customer entered (such as changing country from PR to US, moving data from street2 into street1, standardizing a phone number, etc).