Custom Entity instance

I have got problem with custom entity detection.

Code:Java

 
@EventHandler
public void onInteractCustomEntity(final PlayerInteractEntityEvent e) {
    Player player = e.getPlayer();
    Entity entity = e.getRightClicked();
 
    if(entity instanceof Zombie) {
        EntityZombie zombie = ((CraftZombie) entity).getHandle();
 
        if(zombie instanceof CustomZombie) {
            player.sendMessage("You clicked custom zombie!");
        }
    }
}
 

If i click custom zombie without reload server, all works fine, but after reload server it doesn't work. If i stopped and started server all works fine again. What to do so that after reload the server it still detects custom entity?