Quote Originally Posted by lat9 View Post
That hidden input is most likely being "overwritten" by the base form's address-selection. Note also that the module you identified is used to create both the shipping and billing address, so the warning about needing to select a country might be associated with the zone_country_id[bill] value.
Rather than make store-specific changes to the OPC's templates, you should define a "Zone" that includes only your ship-to country and restrict your shipping module(s) to be active for that defined zone.