Edit a post from frontend. post_tags get saved, but not separated

Ok, found a solution by myself. In the past i saved post_tags with

wp_set_post_terms($pid, array($_POST['post_tags']),'post_tag',false);

Now i save the post_tags with

wp_set_post_tags($pid, $_POST['post_tags']);

and it works. This way is the same method, i use to publish a new post from the frontend. Changed only this, nothing else.