Index: modules/field/field.default.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/field/field.default.inc,v
retrieving revision 1.22
diff -u -r1.22 field.default.inc
--- modules/field/field.default.inc	31 Oct 2009 16:06:35 -0000	1.22
+++ modules/field/field.default.inc	9 Nov 2009 00:46:24 -0000
@@ -17,7 +17,7 @@
   if (isset($form_state['values'][$field_name][$langcode])) {
     $items = $form_state['values'][$field_name][$langcode];
     // Remove the 'value' of the 'add more' button.
-    unset($items[$field_name . '_add_more']);
+    unset($items['add_more']);
   }
 }
 
Index: modules/field/field.form.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/field/field.form.inc,v
retrieving revision 1.32
diff -u -r1.32 field.form.inc
--- modules/field/field.form.inc	1 Nov 2009 14:05:31 -0000	1.32
+++ modules/field/field.form.inc	9 Nov 2009 00:46:25 -0000
@@ -183,7 +183,7 @@
 
     // Add 'add more' button, if not working with a programmed form.
     if ($field['cardinality'] == FIELD_CARDINALITY_UNLIMITED && empty($form_state['programmed'])) {
-      $form_element[$field_name . '_add_more'] = array(
+      $form_element['add_more'] = array(
         '#type' => 'submit',
         '#name' => $field_name . '_add_more',
         '#value' => t('Add another item'),
@@ -236,7 +236,7 @@
     // preview or failed validation)
     $items = array();
     foreach (element_children($element) as $key) {
-      if ($key === $element['#field_name'] . '_add_more') {
+      if ($key === 'add_more') {
         $add_more_button = &$element[$key];
       }
       else {