When you read technical books for fun, do you do the exercises and projects at the end of chapters? I have found that when I read and don't actually use the concepts learned, I tend to forget after some time.
You may want to try converting those questions into byte (heh) sized flashcards and review them from time to time to make sure it sticks. Speaking of which, there's a book called Make It Stick. You might find that interesting as well.