Bug when making collection adds with index

Hello!

Thanks for a great data binding framework. Started to play with it, and sorry if I've misunderstood something but to me it seemed like there's a bug when adding elements with a specific index. I tried to fix that and for me it's working as I expect now, i.e. when you're running e.g.

app.collection.add(new TodoItemModel({todo:"Item not first"}), {at:2})

If i've misunderstood the code, I'd be happy if you could explain how to do things better. 

Cheers