Blog Post
Lief – Previously, notifications were not being delivered in some circumstances for board subscriptions and mentions for several content types, and in this release, that has been corrected.
oh, interesting. I read this as a feature change allowing a user to control whether Moderation Notifications were sent (or not) in their preferences. Since I didn't see that, obviously, in the Follows & Notifications section I made an assumption. :(
Stepping back I see it's in the Found/Fixed section so - it was just a bug.
BUT...that begs my original wonder...what MentionNotificationPreference (or Subscription) controls Moderation Notifications?