Hello. Sorry 
I still don't understand. Perhaps someone else can offer advice? It seems to me the teacher set the subscription in the forum to"forced" so all students got notifications, then the teacher posted the first message in the forum. It makes sense to me that students would receive this message even if they had not posted any replies. Students will always see the tutors' postings - just not the postings of the other students until they make a posting themselves. So I can't see where you think there is a bug?