ConcatenatedProblem

components.ext-component.js

import MyComponent from './my-component';

export default MyComponent.extend({
  
  x: 'extended',
  y: 'extended',
  z: 'extended',
  classNames: 'extended',
  
  internalProperty: "internal",
  
  actions: {
    "setBindedProp": function() {
      this.set('bindedProp', 'nyehe');
    }
  }
});

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  concatenatedProperties: ['x', 'z'],
  attributeBindings: ['x'],
  x: ['original'],
  y: ['original'],
  z: ['original'],
  classNames: ['original'],
  
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  bindedProp: 'change this'
});

styles.app.css

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

.original:before {
  content: "[actual classes on element: " attr(class) "]"; ;
  font-style: italic;
  display: block;
  color: red;
}
.original:after {
  content: "[attributeBinded x value: " attr(x) "]";
  font-style: italic;
  display: block;
  color: red;
}

templates.application.hbs

{{input type='text' value=bindedProp}}
{{ext-component
  x="template"
  y="template"
  classNames="template"
  bindedProp=bindedProp
  actionReceiver=actionReceiver
}}

templates.components.ext-component.hbs

<h2>{{caseDescription}}</h2>
<b>x (concatenated):</b> {{x}}
<br>
<b>y (not concatenated):</b> {{y}}
<br>
<b>z:</b> {{z}}
<br>
<b>classNames:</b> {{classNames}}
<br>
<b>bindedProp:</b> {{bindedProp}}

{{input type='text' value=bindedProp}}
<button {{action "setBindedProp"}}>Press</button>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}