Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.225
diff -u -p -r1.225 form.inc
--- includes/form.inc	14 Sep 2007 10:40:55 -0000	1.225
+++ includes/form.inc	18 Sep 2007 00:41:42 -0000
@@ -1962,7 +1962,8 @@ function _form_set_class(&$element, $cla
 }
 
 /**
- * Remove invalid characters from an HTML ID attribute string.
+ * Prepare an HTML ID attribute string by removing invalid characters and
+ * guaranteeing uniqueness.
  *
  * @param $id
  *   The ID to clean.
@@ -1970,8 +1971,23 @@ function _form_set_class(&$element, $cla
  *   The cleaned ID.
  */
 function form_clean_id($id = NULL) {
+  static $seen_ids = array();
+
   $id = str_replace(array('][', '_', ' '), '-', $id);
-  return $id;
+
+  // In order to guarantee uniqueness, we must check to see if we have seen
+  // this ID before. The first time we see an ID, we leave it alone. Subsequent
+  // sightings get a number appended to the end.
+  while (isset($seen_ids[$id])) {
+    $clean_id = $id .'-'. $seen_ids[$id];
+    $seen_ids[$id]++;
+  }
+  else {
+    $clean_id = $id;
+    $seen_ids[$id] = 1;
+  }
+
+  return $clean_id;
 }
 
 /**