app.js reset event

If you want to smartly update the contents of a Collection, adding new models, removing missing ones, and merging those already present, you now call set (previously named "update"), a similar operation to calling set on a Model. This is now the default when you call fetch on a collection. To get the old behavior, pass {reset: true}.

In you code you use listener to 'reset' event. So you should pass {reset: true} to get what you want.