尝试更改标题内容类型，但它没有任何效果

I'm trying to get a pdf generated by dompdf to download, so I wrote a function that returns dompdf's output, then I changed the headers of the page to include Content-type: application/pdf, the only problem is for some reason is the response header is Content-type: text/html anyways. It is a valid pdf file and everything, so I'm kind of at a loss as to why changing the content type isn't working.

public function couponDownload($location_uniqid = null) {
    $this->autoRender = $this->layout = false;

    // Set data
    $account = $this->Account->getAccount($this->Auth->user('company_id'));
    $data['Location'] = $account['Location'];

    // Set headers      
    header('Content-type: application/pdf');
    header('Content-Description: File Transfer');
    header('Content-Disposition: attachment; filename="coupon.pdf"');
    header('Content-Transfer-Encoding: binary');

    // Generate pdf
    echo $this->Location->generateCouponPdf($data); 
}