masalah session login pada codeigniter

halo temen", saya mau bertanya. Saya membuat login hak akses, saya udah berhasil tapi ada bug, "ketika saya masuk sebagai karyawan dan saya mengedit urlnya menjadi manager, halaman manager tersebut tetap tampil" minta solusinya dong

controller

 <?php if (!defined('BASEPATH')) exit('No direct script access allowed');
	class Login extends MX_Controller
{

function __construct() {
	parent::__construct();
}

public function index(){

	$this->load->view('login/v_login.php');
}

public function cek_login() {

	$user  = $_POST['karyawan_id'];
	$pwd   = $_POST['password'];

	$this->load->model('mdl_login');

	$result=$this->mdl_login->getlogin($user,$pwd)->row();

	if($result)
	{
	 	$sess = array();
			$sess['id']    = $result->karyawan_id;
			$sess['level'] = $result->karyawan_level;
			$sess['is_logged_in'] ='1';
		 	$this->session->set_userdata($sess);
	}
		 	if($this->session->userdata('level') == 'karyawan')	redirect('karyawan/');
		 	elseif($this->session->userdata('level') == 'manager') redirect('manager/');
			elseif($this->session->userdata('level') == 'client') redirect('client/');
			else {
				 	$this->session->set_flashdata('pesan','Oops !!  Username or password error. Please try again');
					redirect('login');
				 }

}

public function logout() {
		$this->session->sess_destroy();
		redirect('login/');

	}

}

models

 <?php
	class Mdl_login extends CI_Model {

function __construct() {
	parent::__construct();
}

	public function getlogin($user,$pwd)
	{
		$this->db->where('karyawan_id',$user);
		$this->db->where('karyawan_password',$pwd);
		$query = $this->db->get('karyawan');

		return $query;

	}

}