Disable SSL at Updaterequest

Hey,

I’m unable to get update-notification since 3.7.1.
My WP-Site runs behind a Proxy, which doesn’t allow any HTTPS connections. But WordPress uses HTTPS to request new updates.
A second installation at another server ran properly, because this installation uses HTTP. The WP-Installations are completely identical, therefore I guess, that there’s a server configuration, but I can’t discover which one..

I’ve already update the config:

define('WP_PROXY_HOST', '...');
define('WP_PROXY_PORT', '80');
define('WP_PROXY_USERNAME', '');
define('WP_PROXY_PASSWORD', '');
define('WP_PROXY_BYPASS_HOSTS', 'localhost, ...');
define('WP_USEPROXY', TRUE);

And set 'sslverify' => false at \wp-includes\class-http.php, line 83.
Also I’ve updated to PHP 5.4.4..

Thank You!