Index: modules/field/modules/list/list.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/field/modules/list/list.module,v
retrieving revision 1.35
diff -r1.35 list.module
141a142,173
>  * Implementation of hook_field_update_forbid(
>  */
> function list_field_update_forbid($field, $prior_field, $has_data) {
> 
>   // A 'list' field stores integer keys mapped to display values. If
>   // the new field has abandoned keys and data data exists for the
>   // abandoned keys, the field will have no way to display them. So,
>   // forbid such an update.
>   if (!empty($prior_field['settings']['allowed_values'])) {
>     $prior_field_allowed = list_extract_allowed_values($prior_field['settings']['allowed_values'], $prior_field['type'] == 'list');
>   }
>   
>   if (!empty($field['settings']['allowed_values'])) {
>     $field_allowed = list_extract_allowed_values($field['settings']['allowed_values'], $field['type'] == 'list');
>   }
>   
>   if ($has_data && $lost_keys = array_diff(array_keys($prior_field_allowed), array_keys($field_allowed))) {
>     // If any data exist for those keys, forbid the update.
>     $query = new EntityFieldQuery();
>     $found = $query
>       ->fieldCondition($prior_field['field_name'], 'value', $lost_keys)
>       ->range(0, 1)
>       ->execute();
>     if ($found) {
>       throw new FieldUpdateForbiddenException("Cannot update a list field to remove keys that have existing data");
>     }
>   }
> }
> 
> 
> 
> /**
162a195,223
> 
>   if (!empty($form_state['values']['field']['field_name'])) {
>     // via manage fields tab
>     $field_name = $form_state['values']['field']['field_name'];
>   }
>   else {
>     // via edit tab
>     $field_name = $form_state['values']['instance']['field_name'];
>   }
>   
>   $prior_field = field_info_field($field_name);
> 
>   if (!empty($form_state['values']['field']['type'])) {
>     // via manage fields tab
>     $new_field = $form_state['values']['field'];
>   }
>   else {
>     // via edit tab
>     $new_field = $prior_field;
>     $new_field['settings']['allowed_values'] = $form_state['values']['field']['settings']['allowed_values'];
>   }
> 
>   try {
>     list_field_update_forbid($new_field, $prior_field, field_has_data($prior_field));
>   }
>   catch (FieldUpdateForbiddenException $e) {
>     form_error($element, $e->getMessage());
>   }
>   
245c306
<     elseif (!$position_keys) {
---
>     elseif ($position_keys) {