I'm not entirely sure that's accurate, is it? I hope not.Well I think this is as designed... the same happens when someone tags you, quoting a post you made in a thread were you are subscribed: you will get 3 notifications for basically the same thing!!!
Hope they can improve this in 2.0
I knew I saw the check in the past and it wouldn't result in a triple notification but I was a little unsure of the quote + tag notifications. Confirmed though, I only received one notification for that.
If a user is both quoted and tagged (though it's one or the other for me, personally), they only get an alert for the quoting, I'm pretty sure.