Hi,
I am using the Joomla Recaptcha plugin API in my custom user registration page (my form is submitted to the joomla registration controller I didn't add user by my self). And I also have a system plugin which validate the captcha answer but the problem is if I have set the default captcha in joomla configuration or in the user registration settings then I always get the false in my system plugin as the answer of the captcha result.

Steps to reproduce the issue

code in my system plugin to check the answer of the recaptcha
$post = JRequest::get('post');

JPluginHelper::importPlugin('captcha');
if(JVERSION < 3)
$dispatcher = JDispatcher::getInstance();
else
$dispatcher = JEventDispatcher::getInstance();

$res = $dispatcher->trigger('onCheckAnswer',$post['recaptcha_response_field']);
if(!$res[0]){
$redirect = 1;
}

Expected result

true

Actual result

false

System information (as much as possible)

PHP Built On Linux dev1 4.4.0-28-generic #47-Ubuntu SMP Fri Jun 24 10:09:13 UTC 2016 x86_64
Database Version 5.7.12-0ubuntu1
Database Collation utf8_general_ci
Database Connection Collation utf8mb4_general_ci
PHP Version 5.6.22-3+donate.sury.org~xenial+1
Web Server Apache/2.4.18 (Ubuntu)
WebServer to PHP Interface apache2handler
Joomla! Version Joomla! 3.6.0 Stable [ Noether ] 12-July-2016 21:14 GMT
Joomla! Platform Version Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
User Agent Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:47.0) Gecko/20100101 Firefox/47.0

Additional comments