Wrong add_template_part implementation and handling of filters

The following implementation seems wrong to me regarding the handling of the filters. The output of the filters is added to the $output variable which seems to be correct. But in the end this variable is not used, but ob_get_clean() is returned. Instead ob_end_clean() should be called and $output should be returned. Current workaround: Use echo in the filter methods, but that’s not how filters should be used.

	protected function add_template_part( $ic_posts, $singles = false ) {
		if ( $singles ) {
			setup_postdata( $ic_posts );
		} else {
			$ic_posts->the_post();
		}
		$output = '';
		ob_start();
		$output .= apply_filters( 'posts_in_page_pre_loop', '' );
		require ( $file_path = self::has_theme_template() )
			? $file_path // use template file in theme
			: POSTSPAGE_DIR . '/posts_loop_template.php'; // use default plugin template file
		$output .= ob_get_contents();
		$output .= apply_filters( 'posts_in_page_post_loop', '' );
		return ob_get_clean();
	}