Sort Ember Array on first load only

I have a form with numerous children which I would like to sort alphabetically.

For this I've used an Array Proxy and the SortableMixin on a computed property, the issue I'm experiencing is when a new item is added to the obeserved property the collection sorts itself again.

What I would like to happen is to have the collection sorted on the first load, and then after that not be sorted.

Here's a jsbin example of the current setup, if you click add a new item will be added to the collection, as soon as you start typing in the new item's input the collection will re-sort which is not ideal.

http://ift.tt/1LFboHw