Index: modules/field_ui/field_ui.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/field_ui/field_ui.admin.inc,v
retrieving revision 1.52
diff -u -r1.52 field_ui.admin.inc
--- modules/field_ui/field_ui.admin.inc	31 May 2010 18:15:20 -0000	1.52
+++ modules/field_ui/field_ui.admin.inc	19 Jun 2010 00:03:20 -0000
@@ -292,7 +292,9 @@
   $js_fields = array();
   foreach (field_ui_existing_field_options($form['#entity_type'], $form['#bundle']) as $field_name => $fields) {
     $field = field_info_field($field_name);
-    $instance = field_info_instance($form['#entity_type'], $field_name, $form['#bundle']);
+    // Get the last existing instance of the same entity type, like
+    // field_ui_existing_field_options() does.
+    $instance = field_info_instance($form['#entity_type'], $field_name, array_pop($field['bundles'][$form['#entity_type']]));
     $js_fields[$field_name] = array('label' => $instance['label'], 'type' => $field['type'], 'widget' => $instance['widget']['type']);
   }
   drupal_add_js(array('fieldWidgetTypes' => field_ui_widget_type_options(), 'fields' => $js_fields), 'setting');