tal, 11 months ago I would guess that one case is "I made a new thread and am OP and want to be notified of all messages to that thread" and the other is "I want to be notified of comments that are children to my own comments".
I would guess that one case is "I made a new thread and am OP and want to be notified of all messages to that thread" and the other is "I want to be notified of comments that are children to my own comments".