Reduced Test Case - Reset State

components.item-viewer.js

import Ember from 'ember';

export default Ember.Component.extend({
  value: false,
  actions: {
    toggle() {
      this.toggleProperty('value');
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  screen: Ember.inject.service(),
  isDesktop: Ember.computed.gte('screen.width', 600),
  /*
  //This strategy makes you retain your state until the value of isDesktop changes, but uses observers.
  watchScreenWidth: Ember.observer('screen.width', function() {
    this.set('isDesktop', this.get('screen.width') >= 600);
  }),
  isDesktop: false,
  */
  columns: Ember.computed('isDesktop', function() {
    Ember.Logger.log('Recomputing columns...', new Date().toISOString());
    return this.get('isDesktop') ? [[{ foo: 1 }, { foo: 3 }],[{ foo: 2 }, { foo: 4 }]] : [[{ foo: 1 },{ foo: 2 },{ foo: 3 },{ foo: 4 }]];
  }),
});

templates.application.hbs

<p>Toggle some items and then resize your screen (or the Ember Twiddle output panel). Even if you don't change from Desktop to Mobile, your items lose their state.</p>
<p>I thought Ember's computed property caching would mean that <code>columns</code> was not recomputed if the value of <code>isDesktop</code> didn't change, but that doesn't seem to be the case.</p>
<br>
{{screen.width}}px ({{if isDesktop "Desktop" "Mobile"}})
<br>
<div style="display: flex">
{{#each columns as |column|}}
  <div>
  {{#each column as |item|}}
    {{item-viewer item=item}}
  {{/each}}
  </div>
{{/each}}
</div>

templates.components.item-viewer.hbs

<button {{action "toggle"}}>
  {{item.foo}} {{if value "on" "off"}}
</button>

twiddle.json

{
  "version": "0.10.6",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.9.0",
    "ember-data": "2.9.0",
    "ember-template-compiler": "2.9.0",
    "ember-testing": "2.9.0"
  },
  "addons": {
        "ember-screen": "0.1.1"
  }
}