_wpsc_updated_visitor_meta_billingcountry and probably the corresponding shipping country, region and state functions check the current region setting when a country update is processed.
If the old country had regions, and the new country does not have regions, the old invalid region value is not cleared.
I think what needs to happen is that if a country is changed, the region and stare values need to be checked and cleared.
Because region & state are typically updated immediately after the country is updated, I don't think this is a huge issue UNLESS a checkout form has a non-standard configuration of shipping same as billing and country/start/region fields