Notifications do not follow subgroup membership

I have a top-level group with projects, subgroups, and sub-sub-groups. If I add a subgroup or sub-subgroup as a member of a top-level project, with all notification settings set to global, and a user’s settings to Watch, they don’t see issues posted to the top-level project, and the project doesn’t appear on the personal notification settings page. However, if the user visits the top-level group page and there sets the notification level to Watch, then they do see the notifications, and it does appear on their personal setting page. This is not the behavior I expected; I would expect that when adding a group to a project its notifications would follow in the same was as adding an individual. Is this a design decision, or a bug? For our use case, it means that every group member has to do this setting individually.