A change was made to the site recently that will now default to notify you when a reply is made to a post that you create or reply to.  People find this convenient since it keeps them from missing a reply to a topic they care about.

If you do not want to be notified when a reply is made to a post you participated in, then when you create a post or reply you need to uncheck the box just above the Post button:

If you are already getting notification emails, you can go to the thread and click "unwatch topic" near the top:

Lastly, you can always go to "My Forum Notifications" under the "Account" menu to see and modify all of your notifications:

Ah ha, so I wasn't just imagining things.  😁

Thanks for the heads up Adam.