Index: wp-admin/includes/post.php
===================================================================
--- wp-admin/includes/post.php	(revision 11505)
+++ wp-admin/includes/post.php	(working copy)
@@ -1334,6 +1334,16 @@
 		$initArray = apply_filters('tiny_mce_before_init', $initArray);
 	}
 
+	if ( empty($initArray['theme_advanced_buttons2']) && !empty($initArray['theme_advanced_buttons3']) ) {
+		$initArray['theme_advanced_buttons2'] = $initArray['theme_advanced_buttons3'];
+		$initArray['theme_advanced_buttons3'] = '';
+	}
+
+	if ( empty($initArray['theme_advanced_buttons3']) && !empty($initArray['theme_advanced_buttons4']) ) {
+		$initArray['theme_advanced_buttons3'] = $initArray['theme_advanced_buttons4'];
+		$initArray['theme_advanced_buttons4'] = '';
+	}
+
 	if ( ! isset($concatenate_scripts) )
 		script_concat_settings();