php：file_exists错误，逗号和空格

I've configured a file download, but in some cases files can't be downloaded. Because the file_exist isn't true, the php code dies and gives me back the defined error message.

Why does the download work fine with a comma OR space in the directory, but fails with BOTH a comma followed with a space?

The file with download error:

$the_download = "/share/Multimedia/Library1/John, Doe/test/cover.jpg";

The files that download ok:

$the_download = "/share/Multimedia/Library1/John,Doe/test/cover.jpg";
$the_download = "/share/Multimedia/Library1/John Doe/test/cover.jpg";

code:

$the_filename = "somefilename.jpg";

    if (file_exists($the_download)) {
        header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');
        header('Content-Disposition: attachment; filename='.basename($the_filename));
        header('Content-Transfer-Encoding: binary');
        header('Expires: 0');
        header('Cache-Control: must-revalidate');
        header('Pragma: public');
        header('Content-Length: ' . filesize($the_download));
        flush();
        readfile($the_download);
        exit;
    }
    else die("File not found<br>" . $the_download); 

you should enclose the filename in the header with double quotes like this :

header('Content-Disposition: attachment; filename="'.basename($the_filename).'");