Long story short, it had long been urban legend that Atari buried thousands of copies of ET for the Atari 2600 after the game flopped. It's considered by many to be possibly the worst console game...ever.
Having had it myself, I can verify it was indeed awful. Worst ever? Not sure about that.
I wonder if they'll find any of the Swordquest games too?
If you're still struggling with this and have held onto the game, maybe the patch they've just released will help? There's nothing specifically mentioning your problem, but maybe it's part of the memory leak issue?