问签名与腾讯签名验证工具得出的结果不一样是怎么回事？

$signArr = array(
    'appid' => $this->appid,
    'mch_id' => $this->mch_id,
    'customs' => $this->customs,
    'out_trade_no' => $this->out_trade_no,
    'transaction_id' => $this->transaction_id,
    'mch_customs_no' => $this->customs,
);

ksort($signArr);
$sign = strtoupper(md5(http_build_query($signArr) . "&key=TwsV7w1GCxH9Ze1JqPNMhvyO9wmkJ9YE"));

var_dump($sign);