OK, I think I got it figured out. When you make each individual post, there's a checkbox at the bottom of the form for email notification. All the posts you made before changing your "edit options" are still checked, so it will take some time before they all go away (until people stop posting on those threads).
Changing the "Edit Options" checkbox only affects new posts. In the future, the email notification box on each new post will not be checked by default, but you can check it if you want. Clear as mud?
