Bug with controller name

[eluser]Unknown[/eluser]
I had controller named "publications.php". Now I will show you its elementary code.

Code:

<?php
if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Publications extends CI_Controller {
    
    function view(){
        echo 1;
    }    

}

When open http://sitename/publications/view it showed me that no such URL found (Denwer error page).
I just renamed the controller to "publish.php" and it worked.

Code:

<?php
if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Publish extends CI_Controller {
    
    function view(){
        echo 1;
    }    

}

Why it is so? Why I can't use publications name?
Version of my CI 2.1.0