reverted:
--- b/core/includes/theme.inc
+++ a/core/includes/theme.inc
@@ -1600,9 +1600,7 @@
       array(
         'data' => array(
           '#prefix' => '<h4' . $header_attributes . '>',
+          '#markup' => $element['#title'],
-          'title' => array(
-            '#markup' => $element['#title'],
-          ),
           '#suffix' => '</h4>',
         ),
         'colspan' => 2,