Problem with preg_replace()

[The Hobo]

I have the following code to create list tags (much like this forum):

function listtag($text) {
    $lststyle = 'style="margin-top: 0px; margin-bottom: 0px;"';

    if (preg_match_all('/\[list=(.*)\](.*)\[\/list\]/siU', $text, $match)) {
        $return = preg_replace('/<br \/>/', '', $match[0]);

        $text = str_replace($match[0], $return, $text);
    }

    $list_tags = array('/\[list=3\](.*)\[\/list\](\r\n|)/siU', '/\[\*\](.*)\[\/\*\]/isU');
    $list_html = array('<ul ' . $lststyle . '>\\1</ul>', '<li>\\1</li>');

    $text = preg_replace($list_tags, $list_html, $text);
    $text = str_replace("</ul><br />", '</ul>', $text);

    return $text;
} 

It works great, except for when there are nested tags, it doesn't seem to grab the inner list tags. Any ideas on how to fix this?