Description:
------------
In some cases, despite changing the proxy of a cURL handle, subsequent transfers will keep using the old proxy.

The bug does not occur with every URL, presumably due to presence or not of "Connection: keep-alive" header in the server response. I was able to reproduce only with some https:// URLs, https://php.net/curl in my attached test script is an example that does reproduce the bug. However http://example.com/ does not reproduce the bug, for example.

cURL version: 7.30.0

Test script:
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<?php

# To reproduce the bug, change 'proxy1.example.com:80' and
# 'proxy2.example.com:80' below with hostname:port of actual proxies. They must
# each resolve to a different IP address.

$ch = curl_init();
curl_setopt($ch, CURLOPT_VERBOSE, TRUE);
curl_setopt($ch, CURLOPT_NOBODY, TRUE);
curl_setopt($ch, CURLOPT_URL, 'https://php.net/curl');
curl_setopt($ch, CURLOPT_PROXY, 'proxy1.example.com:80');
curl_exec($ch);
curl_setopt($ch, CURLOPT_PROXY, 'proxy2.example.com:80');
curl_exec($ch);
curl_close($ch);

?>


Expected result:
----------------
The second curl_exec() call is tunneled through 'proxy2.example.com'.

Output contains:

* About to connect() to proxy proxy2.example.com port 80 (#1)




Actual result:
--------------
The second curl_exec() call is tunneled through 'proxy1.example.com'.

Output contains:

* Re-using existing connection! (#0) with host proxy1.example.com