This is one of a number of related issues, where on joining or leaving a main and sub-group, things do not happen as I expect or think they ought to - whether resolving them is a matter of fixing bug(s), or feature request(s) I'm not sure: they all boil down to an imperfect implementation of the sub-group feature. See also on GMF, topic https://groups.io/g/GroupManagersForum/topic/joining_the_subgroup_directly/69348244
: much of what follows copied from there.
Let me start by stating I expect (and would think correct behaviour):
All concerned ((putative) subscriber and moderators/owners - for both main and sub-group - they may or may not be the same) should be aware of, and have a record of, what has happened, for both main and sub-group.
For joining (or leaving) a main group (only - no-sub-group membership involved), or a sub-group (when already a main group member), however triggered - as normal, with appropriate sequence of e-mails, approvals and activity log entries.
For joining a sub-group, when not a member of the main group:
- on application (by e-mail or web), confirmation e-mail should say that joining sub-group means also joining the main group; on confirming, the main group joining process be gone through first (with appropriate e-mails, approval, and activity logs); then the sub-group process (likewise). If two approvals are needed, perhaps both should be done first, before any other part of part of the joining processes.
- on invitation, if the inviter is not a main group moderator with appropriate permission, then first that approval (to invite to main group) needs be obtained, then invitation e-mail should state that it means to both main and sub-group, and on accepting the invite, the joining processes be gone through for both, as above.
- on direct add, likewise.
On leaving a main group, when also a member of sub-group(s) - confirmation e-mail should state '...and any sub-groups that you a member of', or list them; and then leaving e-mails and activity logs for the sub-group(s) as well as the main group (currently is main group only).
- A Subscribe+ e-mail results - if not already a Main Group member- in them (as Samuel has stated) joining the Main group (only), without any indication to them that they will (confirmation e-mail refers only to the sub-group) - the first they know is the Welcome to Main@~ email. (A subsequent Subscribe+ e-mail results in them joining the sub-group)
- An Invite causes them to be joined to the Sub Group (with e-mails to them and sub-group owner, and an 'accepted invite' activity log), and the Main group - without any notification (e-mail or activity log) - they just (mysteriously) appear on the list of members, and the first the invitee knows about their main group membership is receiving a message. Note that this happens whether or not the inviter (who has to be a sub-group moderator) has the appropriate main group privilege to grant membership: if he doesn't, the first the main group owner will know is if they check the membership list - and realise that there are unexpected (and quite possibly unwanted)
- On leaving a main group, there is a correct (expected) sequence (of logs and e-mails) for this; but membership of sub-groups is just terminated, without any indication (by e-mail or activity log)
While I think - given that sub-group membership is dependent on main group membership - that, except in Samuels's case (joining sub-group leading to main group membership), memberships do change as might be expected , it is very much the case that they are not (completely) notified or logged, and people can find that they have mysteriously joined (or left) groups (sub or main) that they didn't expect to, certainly if they don't know/realise what is going on.