"Excess in non-pipelined read" error with nginx and php-fpm

[eluser]Unknown[/eluser]
Hi,
I am using codeigniter 2.1.3 with Phil Sturgeon's REST Server library and flexiauth. I added memcached on login and logout functions to store and delete login token. When I use these functions with php-fpm and nginx, I get error

Code:

Excess found in a non pipelined read: excess

and some part of the response is cut off.
But, when I use apache + mod_php the same response is returned correctly.
If I comment out the memcached part in those 2 functions, the response works correctly.

Code:

public function logout_get() {
    $user_id = $this->flexi_auth->get_user_id();
    if ( $user_id ) {
       $sip_extension = $this->session->userdata( 'sip_extension' );
    }
      $token = $this->session->userdata('flexi_auth')['login_session_token'];
      $this->load->driver('cache', array('adaptor' => 'memcached'));
      $delete_token = $this->cache->memcached->delete(TOKEN_PREFIX.$token);
      $this->user->makeoffline( $user_id );
      $this->flexi_auth->logout( TRUE );
      $this->session->sess_destroy();
      $this->response( 'Logout successful.', 200 );
}

I can't find anything in the PHP-FPM log which can tell me what the issue could be. Any pointers why it acts differently with apache+mod_php and nginx+php-fpm?

[eluser]Unknown[/eluser]
To eliminate the issue, I ran apache with php-fpm, to reduce the variables. I am running into the issue again. So, the problem is between php-fpm vs mod_php.
I'll take it up in PHP mailing lists too but if somebody has run into this while using codeigniter-restserver library and found a solution, it'll be helpful.