The way forum subscriptions worked in Olympus (3.0) was that a single notification was sent when a new topic or post reply is detected and none after that.
Right now in 3.1.2 an email is being sent and a notification created (if enabled, although by default it is) for every single new topic and reply being done in the subscribed forum. On a busy forum this will result in quite a few emails and notifications.
The topic reply emails being sent state that I am subscribed to the topic, although I'm not, and offers up a way to unsubscribe to the topic, which doesn't do anything as I'm not subscribed to it. This just means the topic reply email template is being used of course.