--- system.module?rev=1.195	2005-02-22 23:58:23.000000000 +0100
+++ system.module	2005-02-23 00:09:00.000000000 +0100
@@ -319,6 +319,11 @@ function system_theme_data() {
     drupal_get_filename('theme', $themes[$key]->name, $themes[$key]->filename);
     drupal_load('theme', $themes[$key]->name);
     $themes[$key]->description = dirname($themes[$key]->filename);
+    if ($themes[$key]->description=='themes') {
+      drupal_set_message(t('Do not place a theme directly under the themes directory. %theme ignored', array('%theme' => $themes[$key]->filename)));
+      unset($themes[$key]);
+      continue;
+    }
     $themes[$key]->owner = $themes[$key]->filename;
     $themes[$key]->prefix = $key;
   }