Oh, is the duplication protection to avoid resubscribing the events in response to each 'onbeforeactivate'? You might want to do this with `node.once()`, or since you have to use `_attach`, to set the 'once' property of the DOM event subscription (see https://github.com/yui/yui3/blob/master/src/event-custom/js/event-target.js#L139)