Index: system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.903
diff -u -r1.903 system.module
--- system.module	21 Mar 2010 03:47:32 -0000	1.903
+++ system.module	26 Mar 2010 20:09:21 -0000
@@ -2671,7 +2671,7 @@
 
   drupal_set_title($question, PASS_THROUGH);
 
-  $form['#attributes'] = array('class' => array('confirmation'));
+  $form['#attributes']['class'][] = 'confirmation';
   $form['description'] = array('#markup' => $description);
   $form[$name] = array('#type' => 'hidden', '#value' => 1);