array_diff 大bug

$aa = array("手机号", "first","keyword1","keyword2","keyword3","keyword4", "remark");
$bb = array("手机号", "first","keyword1","keyword2","keyword3","remark");
$ab = array_diff($bb,$aa);
$abc = array_diff($aa,$bb);
echo '<pre>';
var_dump($ab);　　　　# 错误
var_dump($abc);　　　　# 正确

数组的放法会对 array_diff 的判断有影响