ios在手机游戏中显示文件而不是下载？

I am using the following code to present a file for download to the user... in this case it is a .csv file. Works great in all browsers, BUT in IOS it loads the file in the mobile safari browser. The exact same code works fine for a .zip file (although ios gives the warning it cannot download that type of file).

What gives? Does ios completely disregard the headers or what?

if (is_file($local_path.$file))
{
    //get current ts
    $now = time();

    // set the headers and prevent caching
    header('Pragma: public');
    header('Expires: -1');
    header('Cache-Control: public, must-revalidate, post-check=0, pre-check=0');
    header('Content-Disposition: attachment; filename="'.$now.'_'.$file.'"');   

    // set the mime type based on extension                 
    header('Content-Type: application/octet-stream');
    header('Content-Length: '.filesize($local_path.$file).'');

    //download
    readfile($local_path.$file);

    //delete file
    unlink($local_path.$file);
}