Adding an item to the Cart always returns 2 (qty items)

Hello everybody, as the title,

I use the library cart
And when I added 1 product on the code below:

PHP Code:

$data = array(
        'id'      => 'sku_123ABC',
        'qty'     => 1,
        'price'   => 39.95,
        'name'    => 'T-Shirt',
        'options' => array('Size' => 'L', 'Color' => 'Red')
);

$this->cart->insert($data); 


The result is a multiple of 2 qty as follows:

PHP Code:

Array
(
    [0256a32c98ce49afbe2a4eb8c96c5884] => Array
        (
            [id] => sku_123ABC
            [qty] => 2
            [price] => 39.95
            [name] => T-Shirt
            [options] => Array
                (
                    [Size] => L
                    [Color] => Red
                )

            [rowid] => 0256a32c98ce49afbe2a4eb8c96c5884
            [subtotal] => 79.9
        )

) 


Similarly QTY will add 2 as 4,6,8 ... when I add 1 ITEM into cart