WordPress will ignore your page template settings for the static front page with themes that include their own front-page.php. Here is a quick filter that checks for a page template setting and loads that one instead:
add_filter( 'frontpage_template', 'enable_custom_template_front_page' );
function enable_custom_template_front_page( $template ) {
// Check if a custom template has been selected
if ( get_page_template_slug() )
return get_page_template();
return $template;
}