Concatenated properties in contextual components

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['green-border']
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.blue-background {
  background-color: blue;
}

.red-color {
  color: red;
}

.green-border {
  border-color: green;
  border-style: solid;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>

<p>
  blue-background is not concatenated to red-color, but overwritten by it. red-color is still concatenated with green-backgroun
</p>

{{#with (component "my-component" classNames="blue-background") as |comp|}}
  {{#with (component comp classNames="red-color") as |nestedComp|}}
    {{component nestedComp}}
  {{/with}}
{{/with}}
<br>
<br>

templates.components.my-component.hbs

Hello

twiddle.json

{
  "version": "0.13.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}