use is_a() instead of is_object() in screen_meta(). See #14579

git-svn-id: http://svn.automattic.com/wordpress/trunk@15518 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/template.php

@@ -1634,7 +1634,7 @@ function screen_meta($screen) {
 	if ( is_string($screen) )
 		$screen = convert_to_screen($screen);
 
-	if ( is_object($table) )
+	if ( is_a($table, 'WP_List_Table') )
 		list( $screen_columns ) = $table->get_column_headers();
 	$meta_screens = array('index' => 'dashboard');