为什么php mail（）函数显示主题两次（localhost）

I'm using XAMPP and when I send an email with PHP mail() function the subject comes two times (like "hello, hello").

PHP Code:

$from="me@gmail.com"; 
$to="you@gmail.com";
$subject="hello";
$message="this doesn't work nicely";
$headers = 'From: '.$from."
".
        'Subject: '.$subject."
".
         'Mime-Version: 1.0'."
";

mail($to, '=?UTF-8?B?'.base64_encode($subject).'?=', $message, $headers);

Does anyone know the solution?

Looks like the $headers are the issue here:

$from="me@gmail.com";

$to="you@gmail.com";

$subject="hello";

$message="this doesn't work nicely";

mail($to, '=?UTF-8?B?'.base64_encode($subject).'?=', $message,);