The description of the use of the CURLOPT_POSTFIELDS option should be emphasize, that using POST with HTTP/1.1 with cURL implies the use of a "Expect: 100-continue" header. Some web servers will not understand the handling of chunked transfer of post data.
To disable this behavior one must disable the use of the "Expect:" header with
curl_setopt($ch, CURLOPT_HTTPHEADER,array("Expect:"));