title: Disabled on buttons does not seem to take effect
body: <p>I just started learning ember today. (Trying to do yoember.com) tutorial. Please excuse my newbie questions.</p>
  
  <p>I'm experiencing some issues and I am not sure what I am doing wrong.</p>
  
  <p><strong>Issue:</strong></p>
  
  <blockquote>
    <ul>
    <li>Disabled does not work (it always enables the button)</li>
    </ul>
  </blockquote>
  
  <p><strong>What I am doing:</strong></p>
  
  <blockquote>
    <ul>
    <li>I have a contact page which has email, message and submit button. </li>
    <li>I want to disable the button initially (When there is no email, message)</li>
    </ul>
  </blockquote>
  
  <p>This is what I've done so far:</p>
  
  <p><strong>contact.hbs:</strong></p>
  
  <pre><code>&lt;h1&gt;Contact Page&lt;/h1&gt;
  &lt;form&gt;
    &lt;div class="form-group"&gt;
      &lt;label for="exampleInputEmail1"&gt;Email address&lt;/label&gt;
      {{input type="email" value=emailAddress class="form-control" placeholder="Please type your e-mail address." autofocus="autofocus"}}
      &lt;small id="emailHelp" class="form-text text-muted"&gt;We'll never share your email with anyone else.&lt;/small&gt;
    &lt;/div&gt;
    &lt;div class="form-group"&gt;
      &lt;label for="text"&gt;Text&lt;/label&gt;
      &lt;textarea type="textarea" class="form-control" id="text" placeholder="Text" rows="4" cols="50" value={{message}}&gt;&lt;/textarea&gt;
    &lt;/div&gt;
    &lt;button disabled={{isDisabled}} {{action 'submitButton'}} type="submit" class="btn btn-primary"&gt;Submit&lt;/button&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p><strong>Contact.js</strong></p>
  
  <pre><code>import Route from '@ember/routing/route';
  import { match, not } from '@ember/object/computed';
  
  export default Route.extend({
      emailAddress: '',
      message: '',
      isValid: match('emailAddress', /^.+@.+\..+$/),
      isDisabled: not('isValid'),
  
      actions: {
          submitButton () {
              alert(`Saving of the following email address is in progress:`);
          }
        }
  });
  </code></pre>
  
  <p><strong>Questions:</strong></p>
  
  <p>1) What am I doing wrong? Why is the button always enabled?</p>
  
  <p>2) What is the difference when I do <code>value=emailAddress</code> vs <code>value={{emailAddress}}</code></p>