[Roger Coathup]

@tubruk – this is known issue – take a look at this thread (it covers blog comments and forum responses in the activity stream): https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/replying-to-blog-post-in-the-activity-stream-as-post-comments-rather-than-just-activity-stream-replies/

and for a simple solution from @nuprn1: https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/clarification-needed-on-posting-forum-replies/