On clean install of frappe 13.x.x-develop on Ubuntu, setup the Company in the country of Taiwan. Next, create a New Address, which by default populates the Country field with Taiwan. When I replace country with United States, then save, country field is not updated, remains as Taiwan.
An immediate fix is to open Address List and set the country to United States. Then, all new addresses will have United States as the country.
But, when I create a New Contact, and try linking a New Address, the address has Taiwan as country, and I cannot change it to United States.
Best I recall, earlier versions of ERPNext did not restrict the Country field in the Address Form to the default for the Company.