Well I was afraid I might have insulted you with the suggestion.
But the only reason I did suggest a double check was another user a while back had a similar problem that had the notification enabled via the registration page and all of a sudden new registrations were not getting notified even though it was still enabled on the registration page.
So he never checked a users preferences. Just assumed it was still set.
Bottom line, when you registered, the notification was still appearing as yes but the field would be set to no.
Would be nice to figure out how that can happen.
Possibly a specific from and to version upgrade?(Guessing)
I think Rick worked on that problem. So maybe he can recall what caused it.