PHP Multi Curl - possible bug

$urls = array(
    "http://www.google.com",
    "http://www.yahoo.com",
);

$mh = curl_multi_init();
$activeDownloads = array();

foreach ($urls as $i => $url) {
    $curlHandle = curl_init();
    $key = (int) $curlHandle;

    curl_setopt($curlHandle, CURLOPT_FOLLOWLOCATION, true);
//    curl_setopt($curlHandle, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($curlHandle, CURLOPT_HEADER, 0);
    curl_setopt($curlHandle, CURLOPT_URL, $url);

    $destinationFilepath = '/tmp/download_' . $key;
    $file = fopen($destinationFilepath, "w");
    curl_setopt($curlHandle, CURLOPT_FILE, $file);

    curl_multi_add_handle($mh, $curlHandle);

    $activeDownloads[$key] = array(
        'url' => $url,
        'filepath' => $destinationFilepath,
    );
}

while (true) {

    usleep(50000);

    curl_multi_exec($mh, $running);

    // Call select to see if anything is waiting for us
    $select = curl_multi_select($mh);
    if ($select < 1) {
//        echo 'No download is ready yet' . PHP_EOL;
        continue;
    }

    // Since something's waiting, give curl a chance to process it
    do {
        $status = curl_multi_exec($mh, $running);
        usleep(10000);
    } while ($status == CURLM_CALL_MULTI_PERFORM || $running);


    // Now grab the information about the completed requests
    while ($info = curl_multi_info_read($mh)) {

        $ch = $info['handle'];
        $key = (int) $ch;

        // This outputs all the content correctly when CURLOPT_RETURNTRANSFER is true and the CURLOPT_FILE flag is not set
//        $content = curl_multi_getcontent($ch);
//        var_dump($content);
//        die;

        $download = $activeDownloads[$key];

        $info = curl_getinfo($ch);

        curl_close($ch);

//        print_r($info); die;

        $content = file_get_contents($download['filepath']);

        // This output is cut off, usually at 40960 characters, why?
        echo $content . PHP_EOL;

        echo strlen($content) . PHP_EOL;

        die;
    }
}