--- formfilter.old.module
+++ formfilter.new.module
@@ -119,7 +119,7 @@
     );
     // ...and move all first-level fieldsets there.
     foreach (element_children($form) as $key) {
-      if (!(in_array($key, array('advanced', 'taxonomy'))) && $form[$key]['#type'] && $form[$key]['#type'] == 'fieldset') {
+      if (!(in_array($key, array('advanced', 'taxonomy'))) && $form[$key]['#type'] && $form[$key]['#type'] == 'fieldset' && preg_match("/field_/", $key) == 0) {
         $form['advanced'][$key] = $form[$key];
         unset($form[$key]);
       }