As you may or may not remember, I once reviewed an obscure soundtrack at this blog: Fake-Out by Arthur B. Rubinstein.

I noted that one track sounded like, simultaneously, "You Are My Sunshine" and a precursor to Rubinstein's Blue Thunder. It sounded a little something like this:

What can be said about this? That Rubinstein (or the show's producers) felt that Fake-Out's obscurity would ensure that no one would make the connection? Or maybe this cue was just to get the job on the film (and wasn't actually used) and the composer felt that such an interesting piece of music shouldn't go to waste?

In any event, it's super weird. I wonder if there are any other examples.