Since there's no look-up for IPv6 addresses, they're also restricted. That would explain why some of your US customers are also restricted.

In either case, the following change (applied to each of the /includes/templates/YOUR_TEMPLATE/{product type}/extra_main_template_vars/restrict_digital_downloads.php files) to the jQuery script will ensure that one of the radio buttons in the downloadable product's group is selected during the restriction:
Code:
<script type="text/javascript">
$(document).on ('ready', function(){
  $('<?php echo $download_selectors; ?>').each(function(){
    $(this).removeAttr( 'selected checked' );
    $(this).attr( 'disabled', 'disabled' );
    if ($(this).is( 'input' )) {
      var radioName = $(this).prop( 'name' );
      $(this).siblings('input[name="'+radioName+'"]').eq(0).prop( 'checked', true );

    }
  });
});
</script>
I'll be submitting this change to the plugins for review ...