Changement de JPanel et perte d'écouteur

public class Jeu extends JFrame {
	public PanJeu pan;
	private int width = 600;
	private int height = 600;
	private JLabel LblJouer;
	private JPanel panOuverture;
	
			
	public Jeu() {
		
		
		this.setResizable(false);
		this.setSize(width, height);
		this.setLocationRelativeTo(null);
		this.setTitle("Space Invaders");
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
		pan = new PanJeu(600,600);
		ouverture();
	}
	
	public void switchPan(){
		this.remove(panOuverture);
		this.add(pan);
		this.pack();
		this.setVisible(true);
		pan.setFocusable(true);
	}
	
	
	public void ouverture(){
		panOuverture = new JPanel(new FlowLayout());
		panOuverture.setBackground(Color.BLACK);
		panOuverture.setPreferredSize(new Dimension(width, height));

		// [...] SUITE DU CODE POUR LAFFICHAGE
		
		
		LblJouer = new JLabel("Jouer");
		LblJouer.setOpaque(false);
		LblJouer.setHorizontalAlignment(JLabel.CENTER);
		LblJouer.setVerticalAlignment(JLabel.CENTER);
		LblJouer.setFont(fontSmall);
		LblJouer.setForeground(Color.WHITE);
		LblJouer.addMouseListener( new MouseListener() {
			
			public void mouseClicked(MouseEvent e){
				//System.out.println("oui");
				switchPan();
				LblJouer.removeMouseListener(this);
			}
			public void mouseEntered(MouseEvent e){
				LblJouer.setForeground(Color.GREEN);
			}
			public void mouseExited(MouseEvent e){
				LblJouer.setForeground(Color.WHITE);
			}
			public void mousePressed(MouseEvent e){
			}
			public void mouseReleased(MouseEvent e) {
			}
        } );
		
		//[...]
		
		
		this.add(panOuverture);
		this.pack();
		this.setVisible(true);
		//panOuverture.setFocusable( true );
	}
	

public class PanJeu extends JPanel{
	Timer timer;
	private BufferedImage imCanon;
	private BufferedImage imTir;
	private boolean tir;
	private Point coordCanon;
	private Point coordTir;
	private Alien alien;
	private final int bordD;
	private final int bordG;
	private final int bordH;
	private final int bordB;
	private int vitesse = 800;
	private Timer destruction;
	private Timer moveAlien;
	private int nbAliens = 55;
	private boolean actionDead = false;
	private boolean actionMoveAlien = false;
	private int move = 10; //pour indiquer dans quel sens se déplace les aliens
	private int vies = 3;
	private int score = 0;
	private int imMove = 2; //pour changer l'image des aliens quand ils bougent
	private Font customizedFont;

	public PanJeu(int width,int height) {
		// TODO Auto-generated constructor stub
        alien = new Alien(this,1,width/7,height/7);
		setBackground(Color.BLACK);
		setPreferredSize(new Dimension(600, 600));
		bordD =(int)(width/1.0734);
		bordG =(int)(width/28.49);
		bordH = (int) (height/9);
		bordB = (int) (height/1.05)-5;
        
        tir = false;
        double y = height/ 1.12;
        coordCanon = new Point( (width/2)-19, (int)y );
        
		timer = new Timer(30, new ActionListener() {

            public void actionPerformed( ActionEvent e ) {
                repaint();
            }
        } );
		timer.start();
		destruction = new Timer(200, new Destruction());
		moveAlien = new Timer(vitesse, new MoveAlien());
		
		addKeyListener( new KeyAdapter() {

            public void keyPressed( KeyEvent e ) {
                switch ( e.getKeyCode() ) {
                    case KeyEvent.VK_LEFT:
                    	if (coordCanon.x+7 >= bordG){
                        	coordCanon.x-=7;
                    	}
                        break;
                    case KeyEvent.VK_RIGHT:
                    	if (coordCanon.x+7 <= bordD){
                    	coordCanon.x+=7;
                    	}
                        break;
                    case KeyEvent.VK_SPACE:
                    	System.out.println("BON");
                    	tirer();
                    	break;
                }
            }
        } );
	}

         //[...]

   }