title: Base template doesn't render other regions by default when calling this.render('template')
body: <p>Been stuck on this for a few hours...I'm having a weird behaviour when using iron:router (1.0.1) and trying to render a 403 access forbidden template inside my base template:</p>
  
  <p>I have a default template set using iron-router default options like this</p>
  
  <pre><code>Router.configure({
        layoutTemplate: 'basicLayout',
        yieldRegions: {
          'header': {to: 'header'},
          'footer': {to: 'footer'}
        }
      });
  
  Router.plugin('dataNotFound', {notFoundTemplate: 'notFound'});
  </code></pre>
  
  <p>Here it is my template: </p>
  
  <pre><code>&lt;template name="basicLayout"&gt;
      &lt;header&gt;
          {{&gt; yield 'header'}}
      &lt;/header&gt;
      &lt;div id="main"&gt;
          {{&gt; yield}}
      &lt;/div&gt;
      &lt;footer class="sticky-footer"&gt;
          {{&gt; yield 'footer'}}
      &lt;/footer&gt;
  &lt;/template&gt;
  </code></pre>
  
  <p>Everything works as expected and I'm able to render individual templates inside this layout by defining routes in the normal way: </p>
  
  <pre><code>Router.route('ordersList', {
      path: '/orders',
      template: 'ordersList',
      waitOn: function () {
          Meteor.subscribe('Orders');
      }
  });
  </code></pre>
  
  <p>However, when I do: </p>
  
  <pre><code>Router.onBeforeAction(function () {
  
          if (Roles.userIsInRole(Meteor.userId(), ['delivery'])) {
              this.next();
          } else {
              this.render('accessDenied');
          }
      }
      , {
          only: 'ordersList'
      });
  </code></pre>
  
  <p>It only renders the template in the main region, but no header or footer are rendered (they are there, but empty).</p>
  
  <p>If I force the rendering for the regions, using </p>
  
  <pre><code>this.renderRegions();
  this.render('accessDenied');
  </code></pre>
  
  <p>Everything works as expected, however this seems a little bit weird -and redundant- usage to me, it should just be enough without calling <code>this.renderRegions()</code>. Is this a bug or a feature? Or is there anything I'm doing wrong? I saw many examples that just use <code>this.render('templateName')</code></p>