Thanks, Simon! I moved your topic into a reply to the feature request because I agree with @sam it belongs here.
You’ve done a great job updating the issue raised in the OP here, given more recent changes to the invite system since this topic was created. The tl;dr is that admins are allowed to create invites whereby the invitee is added to one or more groups immediately as they create their accounts. Regular members who are group owners cannot.
It feels to me like it should be possible for site owners to grant access to the “Add to groups” pulldown when creating an invite, perhaps using a new allowed_by_group setting? If it’s allowed, then they can only select groups that they are owners of.
I can imagine use cases though when site owners might not want to allow it. If it is not allowed, then the invite button should not be shown on the group page for that member even if they are a group owner. Maybe removing it would be the right first move to make, so the UI is at least consistent.
