Actionscript :: Flash - Stops Functioning When Navigate Away From A Certain Frame

A friend of mine wants to have some navigation-based mc links in frame 1, then nav to a certain frame, and then have a "back" button. When the nav mc links are clicked, the timeline skips to a given frame label.
Pretty simple.

Most of the links have the same nav mc in them, so when I nav to them, I can also access any of the other frames via something like:

linkg.Contact_btn.addEventListener(MouseEvent.CLICK,Contact_btn_clicked);
function Contact_btn_clicked(e:MouseEvent):void{
gotoAndStop("ContactPage");
}

The code above is in the first frame, and it is on it's own layer which spans the entirety of the frames in the project, so I would think that these function definitions would persist. But, when I go to a specific link, which does not have the nav mc in it, and then hit that particular frame's "back" button, all of my function definitions are gone, even though the nav mc links are now present, and as I mentioned the listeners should be active.