__destruct called twice in CodeIgniter - php

Question

First: I've already reviewed all the questions I can find about __destruct() and CodeIgniter, and none seem to address the same issue I'm seeing.
Right. That aside. I'll show code first, as the problem will make more sense after reading. (N.B.: some code redacted, but nothing important to the question. The Billing::index function however, is comprises only one space character in production as well as here)
application/core/MY_Controller.php
class MY_Controller extends CI_Controller{
public $view = '';
public $data = array();
public $template = '';
function __destruct(){
if(!is_null($this->template) && ($this->template == '')){
$this->template = 'public';
}
if($this->view == ''){
$this->view = $this->uri->segment(1,'index').'/'.$this->uri->segment(2,'index');
}
if(!is_null($this->template)){
echo $this->load->view('templates/'.$this->template.'/top',$this->data,true);
}
echo $this->load->view('views/'.$this->view,$this->data,true);
if(!is_null($this->template)){
echo $this->load->view('templates/'.$this->template.'/bottom',$this->data,true);
}
}
}
class MY_ProtectedController extends MY_Controller{
function __destruct(){
parent::__destruct();
}
}
application/controllers/billing.php
class Billing extends MY_ProtectedController{
public function index(){ }
}
This, loads perfectly. The main "billing" page is just HTML, so the destructor fires the right template and view.
However, I would love to remove the redundant public function index(){ }, as it really does nothing.
So if I remove that from application/controllers/billing.php so that it's just
class Billing extends MY_ProtectedController{ }
and visit /billing, I get the output I want, however, I get it twice.
If I do some test echos, MY_ProtectedController::__destruct() is called once, but MY_Controller::__destruct is called twice.
My question is: why is this the case, and can it be stopped?
I'm not super familiar with CI core, and I figure that by the time I dig far enough to find the controller instantiation, someone here has probably already got an answer. Will of course update this if my own digging turns anything up.

Answer 1

Solution ended up being fairly simple - but credit for spotting this goes to one of our other programmers.
If I put some code in my 404 route to prevent the auto-destructor from running, I only get one set of output.
class Index extends MY_PublicController {
public function not_found(){
$this->cancel_destruct = TRUE;
}
}
class MY_Controller extends CI_Controller{
$this->cancel_destruct = FALSE;
function __destruct(){
if(!$this->cancel_destruct){
[...]
}
}
}