--- modules/menu/menu.admin.inc	2010-10-20 09:40:59.000000000 +0200
+++ modules/menu/menu.admin.inc	2010-10-28 22:48:37.812500000 +0200
@@ -385,6 +385,13 @@ function menu_edit_item_validate($form, 
   if (!trim($item['link_path']) || !drupal_valid_path($item['link_path'], TRUE)) {
     form_set_error('link_path', t("The path '@link_path' is either invalid or you do not have access to it.", array('@link_path' => $item['link_path'])));
   }
+  elseif (preg_match('/node\/(\d+)/', $item['link_path'], $matches) && ($type = db_query("SELECT type FROM {node} WHERE nid = :nid", array(':nid' => $matches[1]))->fetchField())) {
+    list($menu_name, $plid) = explode(':', $item['parent']);
+    $type_menus = variable_get('menu_options_'. $type, array('main-menu' => 'main-menu'));
+    if (!in_array($menu_name, $type_menus)) {
+      form_set_error('parent', t("The %menu_title menu cannot contain links to the path '@link_path'.", array('%menu_title' => substr($form['parent']['#options'][$menu_name .':0'], 1, -1), '@link_path' => $item['link_path'])));
+    }
+  }
 }
 
 /**