Index: list/list.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/field/modules/list/list.module,v
retrieving revision 1.35
diff -u -r1.35 list.module
--- list/list.module	11 Oct 2010 19:57:00 -0000	1.35
+++ list/list.module	14 Oct 2010 17:54:20 -0000
@@ -69,6 +69,7 @@
 
   $form['allowed_values'] = array(
     '#type' => 'textarea',
+    '#disabled' => $has_data,
     '#title' => t('Allowed values list'),
     '#default_value' => $settings['allowed_values'],
     '#required' => FALSE,