not sure if people has posted this earlier but found out that in motionEnded:(UIEventType)motion withEvent:(UIEvent*) we supposed to call below and NOT [self.undoManager undo].

//Only respond to shake events.
if (event.type == UIEventSubtypeMotionShake){
[self.weightHistory undo];
}

The way it says in the book doesn't work so instead if you call

[sel.weightHistory.undoManager undo] will work without giving any Alert to the user.

Thanks seems like my app is working. Only need to test the actual "Conflict" logic which is most disturbing to me!