Just answer this now because I've just made another change to it, for anyone that uses this feature.
Yeah, you only get one new post per subscribed to thread, until you visit the forum again. That was the way it was always supposed to work but didn't.
The other change is that if you want to add new topic subscriptions you will have to verify your e-mail address (once) by receiving a verification e-mail. It will tell you what to do when you subscribe to a thread or make a post with the relevant option selected.