Description:
------------
cURL seems to always ignore the last header set through CURLOPT_HTTPHEADER. When I inspect outgoing requests with Wireshark, it consistently shows that the last header in an headers array provided to cURL gets ignored. For the headers provided in the 'Test Script' field, this is what Wireshark reports (The 'X-Remove' header is gone) :

POST [REMOVED] HTTP/1.1
Host: [REMOVED]
Accept: */*
Accept-Encoding: application/xml
X-External-User-ID: 1
X-Territory-ID: 9b0a8426-1493-4997-aab0-2d0de736225a
X-Company-Name: Company Name
X-File-Quality: 1
X-File-Type: JPG
X-Filename-Prefix: prefix
X-Title: Title
Authorization: Basic dGVzdDp0ZXN0
X-Trace: 2B2B1AB863BA48CFF980DCE0B5CD3C3FE7DD4E68390B4A407CEEBFEBC601

If I take out the 'X-Remove' header, then cURL will ignore the 'Authorization' header. 

Test script:
---------------
$headers = array(
  'X-External-User-ID: 1',
  'X-Territory-ID: 9b0a8426-1493-4997-aab0-2d0de736225a',
  'X-Company-Name: Company Name',
  'X-File-Quality: 1',
  'X-File-Type: JPG',
  'X-Filename-Prefix: prefix',
  'X-Title: Title',
  'Authorization: Basic dGVzdDp0ZXN0',
  'X-Remove: This header will be removed by curl',
);

$curl = curl_init();
  curl_setopt_array($curl, array(
    CURLOPT_URL => $url,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_ENCODING => "application/xml",
    CURLOPT_MAXREDIRS => 10,
    CURLOPT_TIMEOUT => 3,
    CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
    CURLOPT_CUSTOMREQUEST => $method,
    CURLOPT_HEADER => 1,
    CURLOPT_HTTPHEADER => array_values($headers)
  ));