Index: modules/excerpt/excerpt.module
===================================================================
--- modules/excerpt/excerpt.module	(revision 79)
+++ modules/excerpt/excerpt.module	(working copy)
@@ -50,10 +50,11 @@
   }
 
   if ($form['type']['#value'] .'_node_form' == $form_id && variable_get('excerpt_'. $form['type']['#value'], 1)) {
+    $form['#node']->teaser == node_teaser($form['#node']->body) ? $default = '' : $default = $form['#node']->teaser;
     $form['teaser'] = array(
       '#type' => 'textarea',
       '#title' => t('Teaser'),
-      '#default_value' => $form['#node']->teaser,
+      '#default_value' => $default,
       '#cols' => 60,
       '#rows' => 6,
       '#weight' => variable_get('excerpt_wt_'. $form['type']['#value'], 0),