Index: wp-admin/includes/post.php
===================================================================
--- wp-admin/includes/post.php	(revision 1310)
+++ wp-admin/includes/post.php	(working copy)
@@ -1339,6 +1339,18 @@
 	if ( 'en' != $language )
 		include_once(ABSPATH . WPINC . '/js/tinymce/langs/wp-langs.php');
 
+	// strip empty button lines
+	$_buttons = array();
+	foreach ( array(1, 2, 3, 4) as $k ) {
+		if ( $initArray['theme_advanced_buttons' . $k] !== '' )
+			$_buttons[] = $initArray['theme_advanced_buttons' . $k];
+	}
+	for ( $k = 0; $k < 4; $k++ ) {
+		$initArray['theme_advanced_buttons' . ($k+1)] = isset($_buttons[$k])
+			? $_buttons[$k]
+			: '';
+	}
+
 	$mce_options = '';
 	foreach ( $initArray as $k => $v )
 	    $mce_options .= $k . ':"' . $v . '", ';