Prohibit the creation of a new alias during node_save()

Hello everyone!

alias template [random:hash:haval128,5]

When i try to update existed node by node_save() node alias will be changed.
If i try to use
$node->path['pathauto'] = FALSE;
Alias ​​will not change but notice will be appeared

Notice: Undefined index: alias in path_node_update() (line 204 in #####/modules/path/path.module).