That's happened to me my entire life and it's mostly when I see the movies at the movie theater. I don't remember most of the movies I've seen at the theater. I'm not sure why. I didn't remember any of the Lord of the Rings movies, there were huge chunks missing that I found out about only when I saw them on DVD. Same with Harry Potter and lots of others. They were good movies so it couldn't have been that, I just blame it on bad memory and something that happens to me at the theater.