It seems that if you release an update to a resource the thread is marked as 'unread' after it creates a post from you and you won't receive any alerts after this unless you actually go and read the thread.
If the thread is unread already, it will remain unread. If it's read, we'll keep it read. I suspect that's what happened here. I'm going to call this as designed unless you have a particular example where you know the thread was already marked as read and it became unread. (In that case, don't read the thread with the account in question but report it as I'd need to see what the read date was in the DB.)