form_submit() does not post

I would guess it actually has to do with your form_validation library. This is a known challenge with WireDesignz' HMVC code. According to his docs at BitBucket:

When using form validation with MX you will need to extend the CI_Form_validation class as shown below,

Code:

<?php
/** application/libraries/MY_Form_validation **/
class MY_Form_validation extends CI_Form_validation
{
   public $CI;
}

before assigning the current controller as the $CI variable to the form_validation library. This will allow your callback methods to function properly. (This has been discussed on the CI forums also).

Code:

<?php
class Xyz extends MX_Controller
{
   function __construct()
   {
       parent::__construct();

       $this->load->library('form_validation');
       $this->form_validation->CI =& $this;
   }
}

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