[MPDev]

I think you can remove some errors with an extra check:

// HACK : END : AUTO TAG

        if ( $post['taglist'] )
        {
            fetch_valid_tags($dataman->thread, $post['taglist'], $tag_errors, true, false);
            if ($tag_errors)
            {
                foreach ($tag_errors AS $error)
                {
                    $dataman->error($error);
                }
            }
        }
    }

This way it doesnt try to process blank taglists.

Note: Didnt see the plugin before making this suggestion.