=== modified file 'sites/all/modules/hierarchical_select/hierarchical_select.module'
--- hierarchical_select.module	2011-02-20 11:16:54 +0000
+++ hierarchical_select.module	2011-04-14 05:24:26 +0000
@@ -94,6 +94,15 @@ function hierarchical_select_flush_cache
 function hierarchical_select_form_alter(&$form, $form_state, $form_id) {
   if (_hierarchical_select_form_has_hierarchical_select($form)) {
     $form['#after_build'][] = 'hierarchical_select_after_build';
+
+    // Ensure 'language' gets POSTed; we need it in the AJAX callback.
+    if (isset($form['language']) && !empty($form['language']['#disabled'] )) {
+      $form['language__hs_moved'] = $form['language'];
+      $form['language'] = array(
+        '#type' => 'hidden',
+        '#value' => $form['language']['#default_value'],
+      );
+    }
   }
 }