按标签搜索Twitter API v1.1-不返回旧结果

我正在使用新的api Twitter（1.1版）搜索标签，它可以获得一些结果。但对于较旧的推文，不会返回结果。

我的代码：

    $this->load->library("TwitterAPIExchange", $settings);
    /** Perform the request and echo the response **/
    $twitter = new TwitterAPIExchange($settings);
    /** URL for REST request, see: https://dev.twitter.com/docs/api/1.1/ **/
    $url = "https://api.twitter.com/1.1/search/tweets.json";
    $requestMethod = "GET";
    //hashtag
    $hashtag = "#vmb2012";
    //Method search parameters GET
    $getfield = "?q=$hashtag&result_type=mixed&count=100";
    //Counter tweets
    $count = 0;
    /** Search global tweets for a hashtag **/
    $result = json_decode( $twitter->setGetfield($getfield)->buildOauth($url, $requestMethod)->performRequest() );      
    if(!empty($result))
    {
        //increases the qty of tweets
        $count = isset($result->statuses) ? count($result->statuses) : 0;
        //if you have more results, performs the query again                                
        while($result->search_metadata && isset($result->search_metadata->next_results))
        {
            //search parameters of the next result
            $getfield = $result->search_metadata->next_results;
            $result = json_decode( $twitter->setGetfield($getfield)->buildOauth($url, $requestMethod)->performRequest() );
            $count += count($result->statuses);             
        }                   
    }
    echo "Hashtag: ".$hashtag." <br>";
    echo "Counter: ".$count;

有人能帮我吗？