Notifications not sent to group members

In my gitlab CE install, I have all my users as members of groups, and all the projects they can access are organized under those groups. However, these users don't receive activity email notifications. Of particular note, if someone comments on a commit, the committer does not get notified. This makes gitlab essentially unusable as a code review tool. If I make people explicit members of the project, then the notifications seem to work as expected, but that makes user management substantially more cumbersome, which makes me question the point of even having groups. Am I missing something, or this actually a bug? It seems like a bug...