Size of file downloaded on Github differs from headers with PHP and protocol 1.1

test.php

<?php

//Smaller file 1M: $test_url = 'https://github.com/mickaelperrin/phantomJS/releases/download/2.1.1/file.txt.bz2';
$test_url = 'https://github.com/medium/phantomjs/releases/download/v2.1.1/phantomjs-2.1.1-linux-x86_64.tar.bz2';

function test_result($result, $http_response_header) {
    $result_content_length = strlen($result);
    $header_content_length = null;
    foreach ($http_response_header as $header) {
        if (preg_match('{^content-length:\s*(.+?)\s*$}i', $header, $match)) {
            $header_content_length = $match[1];
            break;
        }
    }

    if ($result_content_length == $header_content_length ) {
        echo "\n[SUCCESS] Content-length are matching";
        echo "\nContent-length: $header_content_length";
    } else {
        echo "\n[FAIL] Content-length are different";
        echo "\nDownloaded length: $result_content_length";
        echo "\nReported length: $header_content_length";
    }
}

echo "\nFirst test with context HTTP protocol 1.1";
$context_1_1 = array (
    'http' =>
        array (
            'protocol_version' => 1.1,
        ),
);

$ctx = stream_context_create($context_1_1);
$result = file_get_contents($test_url, false, $ctx);
test_result($result, $http_response_header);

echo "\nSecond test with context HTTP protocol 1.0";
$context_1_0 = array (
    'http' =>
        array (
            'protocol_version' => 1.0,
        ),
);

$ctx = stream_context_create($context_1_0);
$result = file_get_contents($test_url, false, $ctx);
test_result($result, $http_response_header);