Description:
------------
The aforementioned RFC deals with how to encode filenames when sending files as part of a POST request. If PHP receives a request from a client that implements this RFC, and the filename has special characters, the uploaded files will be lost ($_FILES will be empty), and a warning will be produced:

PHP Warning:  File Upload Mime headers garbled in Unknown on line 0

It doesn't matter if you put Apache, or nginx in front of PHP, or use the built in webserver.

http://tools.ietf.org/html/rfc2231

Test script:
---------------
Create an index.php file:

<?php

header('content-type', 'application/json');
echo json_encode($_FILES);

Launch the webserver with php -S localhost:9000.

Use this python script that uses the requests library to make an RFC 2231 compliant request:

import requests

filename = 'fårikål.txt'
destination = 'http://localhost:9000'
files = { filename: 'hello world' }

res = requests.post(destination, files=files)
print(res.status_code, res.text)

Expected result:
----------------
{
  "får": {
    "name": "får.txt",
    "type": "text/plain",
    "tmp_name": "/tmp/phpuXCXkF",
    "error": 0,
    "size": 12
  }
}

Actual result:
--------------
200 []

(empty result due to the warning, and status code 200)