No, I haven't tried it ... I told you to remove it because it's wrong regardless of the problem that you're having - get_instance() gets an instance of your controller, and you're calling it from that same controller's constructor, which in turn is the place where a lot of stuff is loaded, so it made sense that it could break something.
My only guess left is that your browser simply doesn't send a cookie to your image URLs, thinking that they're static images, which causes the session handler to force-create a new session.
