Anyway, here's some code -

	IF ($this->form_validation->run()){ //<---Form validation.
		IF (!$this->User->login( //<---Attempt to log in the user with POST data
			addslashes(strtolower($this->input->post('username', TRUE))), //<-Username
			addslashes($this->input->post('password', TRUE)), //<- Password
			$this->getIP())){ //<-IP
			/*If the login failed stuff goes here bla bla not relevant.*/
		} ELSE {
			SWITCH($this->User->stale('Permissions')){ //<- This works
				CASE 'ADMIN':
					redirect('Admin');
					BREAK;
				/*Some other stuff but not relevant*/
			}
		}

I've set a breakpoint in the Admin controller class constructor :

	CLASS Admin EXTENDS CI_Controller{
		public FUNCTION __construct(){
			PARENT::__construct(); //<-This gets hit.
			$this->load->model('User_Model', 'User'); //<- So does this, but when the $_SESSION value appears in the Variables view, it only has a single value in it.
			$this->User->ID = $this->session->UserID;
			/*Some other stuff that goes here; again, not relevant.*/
		}
	}

Then there's also where the session data is being set; within the `User_Model` `Login( ... )` method -

	CLASS User_Model EXTENDS MY_Model{ //<----- MY_Model is just an extension of the CI_Model class that lets me use some of our Database stuff. Testing shows that it all checks out.
		public FUNCTION login($userName, $password, $IP){
			$row = $this->database->get_where('users', ARRAY('UserName' => $userName))->row_array()['UserName'];
			IF (!ISSET($row)){
				/*bla bla bad username handle it.*/
			} ELSE {
				/*Check password against username*/
				IF (/*Stuff*/) {
					/*Bla bla bad password handle it.*/
				} ELSEIF(/*check for already logged in*/){
					/*Bla bla logged in already handle it.*/
				} ELSE {
					/*Login was successful and there was much rejoicing (yaaay) handle it...*/
					/*Then I try and set the session values so that they are accessible after the redirect to the Admin controller:*/
					$this->session->UserID = $row['UserID'];
					/*and many others which aren't persisting*/
				}
			}
	}