Threads which are posted only in groups shouldn't be propagated to home-feeds of non-subscribers. Currently they do if friend of non-subscriber likes or comments there.
Cases:
Post is made both to user's feed and to one or several groups. Like or comment propagates the post to friends' home-feeds
Post is made ONLY to one or several groups. Likes and comments DO NOT propagate post to those who are not member of at least one of these groups
Threads which are posted only in groups shouldn't be propagated to home-feeds of non-subscribers. Currently they do if friend of non-subscriber likes or comments there.
Cases: