奇怪的邮件发送问题。。怎么没主题啊

<?php
if(isset($_POST['emailtitle']))
{
$to = "[email protected]";
$subject = $_POST['emailtitle'];
$message = $_POST['emailcontent'];
$from = "[email protected]";
$headers = "From: $from";
mail($to,$subject,$message,$headers);
echo "<script>window.location.href='xxxxxxx';</script>";
}?>邮件发送成功，但是主题没有，，
我echo subject有值的啊，如果我固定subject内容，主题有的，，现在换了变量怎么就不行了呢