Kohana columns with extra columns not loading

I am using Kohana v3 with database and ORM. I found a good question that helps me add and read extra columns in pivot tables: Kohana 3.0.x ORM: read extra columns in pivot tables

I have 2 pivot table with an extra column. One of these works is excellent, but I'm stuck in suspense with the second.

Get 2 tables, applications and partners plus my pivot table with the following ORM models:

class Model_Application extends ORM
{

    protected $_has_many = array(
        'partners'=>array(
            'model'=>'partner',
            'through'=>'partners_applications',
            )
        );
}

//AND

class Model_Partner extends ORM
{

protected $_has_many = array(
    'applications' => array(
        'model'=>'application',
        'through'=>'partners_applications',
        )
    );

}

//plus my pivot table ORM model

class Model_Partners_applications extends ORM
{

    protected $_belongs_to = array(
            'partner' => array(),
            'application' => array()
        );
}

When i try to get

$instance = ORM::factory('partners_applications',array('partner_id' => $this->partner,'application_id' =>   $this->application))->find();

Kohana continues to say:

ErrorException [ Fatal Error ]: Class 'Model_Partners_applications' not found

I have tested model name constructions three times, but I cannot find the error. In the debugging part of the Kohana environment, my first two models are loaded, but not a pivot table.

Any ideas?