Ion Auth login attempts exceeded

I'm using Ben Edmund's Ion Auth for user authentication.

In it's config file, my settings are:

PHP Code:

$config['track_login_attempts'] = TRUE;   
$config['track_login_ip_address'] = TRUE;
$config['maximum_login_attempts'] = 5;
$config['lockout_time'] = 600; 


In my login method, I have this piece of code:

PHP Code:

$ip = $this->input->ip_address();
if ($this->ion_auth->is_max_login_attempts_exceeded($ip)) {
  $this->render_page('auth/login_attempts_exceeded');    
} 


Unfortunately, it doesn't work. I can try to login numerous times with different usernames and password, but it will never show the page with information about a lock-out.
I want to lock out the user if there are too many unsuccessful login attempts from his ip address.
How can I accomplish that?