title: Polymer repeating template issues
body: <p>Sorry for the vague title, I wasn't sure how to phrase what I mean.</p>
  
  <p><strong>Background:</strong> I'm making a single page application for my company, I was building in polymer 0.56, and am just trying to upgrade to 1.0.</p>
  
  <p><strong>Issue:</strong> When cloning content (clean HTML) into my main "view" div, some polymer elements (buttons) are repeatedly nesting themselves causing UI bugs shown:</p>
  
  <p><img src="https://i.stack.imgur.com/3q9M1.png" alt="Logout button with 2 UI buttons"></p>
  
  <p><strong>The generated code:</strong></p>
  
  <p><img src="https://i.stack.imgur.com/Uspad.png" alt="The bad generated UI code"></p>
  
  <p>This only happens when I .clone() the content, or use .innerHTML to copy it into the view div. e.g.</p>
  
  <pre><code>mainDiv.append($(cleanHTML).clone());
  </code></pre>
  
  <p>And the odd bit is that this issue does not occur when the following is used:</p>
  
  <pre><code>mainDiv.append(cleanHTML);
  </code></pre>
  
  <p><strong>This gives:</strong></p>
  
  <p><img src="https://i.stack.imgur.com/kEuNW.png" alt="What the button should look like">
  <img src="https://i.stack.imgur.com/Pcmgn.png" alt="Good code"></p>
  
  <p>The main div is always cleaned before I add anything. I want to avoid directly using the object cleanHTML if possible (hence why I was trying to .clone()) does anyone have any idea what is causing this?</p>