title: Updating 'paper-item's inside 'paper-listbox' by way of 'dom-repeat' and data binding fails
body: <p>Note: This question is regarding an old version of polymer. Google engineers drive to make quick breaking updates to the polymer package coupled with the fact that at the time they weren't dogfooding it means that the issue is obsolete.</p>
  
  <p>The initial data binding to variable journal_tags in the ready function works and I get the three options 'meeting', 'payment' and 'general_message' to show up. The problem arises when I try to introduce a new option by changing the 'new_tag' variable. 'new_tag' is changed by data binding in a different polymer element.</p>
  
  <p>When the observer function 'add_new_tag' that monitors changes to 'new_tag' gets called these are the console logs: </p>
  
  <pre><code>0meeting
  1payment
  2general_message
  3tada
  </code></pre>
  
  <p>Therefore 'journal-tags' is changed. But the problem is that the 'paper-item' options in the 'paper-listbox' remain the same initial 'meeting', 'payment', 'general_message', even though I expected changes to 'journal-tags' to add the 'tada' option.</p>
  
  <p>This is the code:</p>
  
  <pre><code>&lt;dom-module id="journal-entry"&gt;
    &lt;template&gt;
      &lt;paper-dropdown-menu label="Choose tag"&gt;
          &lt;paper-listbox class="dropdown-content"&gt;
              &lt;template is="dom-repeat" items="{{journal_tags}}"&gt;
                  &lt;paper-item&gt;
                      {{item.tag}}
                  &lt;/paper-item&gt;
              &lt;/template&gt;
          &lt;/paper-listbox&gt;
      &lt;/paper-dropdown-menu&gt;
      &lt;paper-textarea label="journal_entry_text_area"&gt;
      &lt;/paper-textarea&gt;
    &lt;/template&gt;
    &lt;script&gt;
    (function() {
      'use strict';
  
      Polymer({
        is: 'journal-entry',
          properties:{
              new_tag:{
                  type:String,
                  notify:true,
                  observer:'add_new_tag'
              },
              journal_tags:{
                  type:Object,
                  notify:true
              }
          },
          ready : function(){
              this.journal_tags=[
                  {tag:'meeting'},
                  {tag:'payment'},
                  {tag:'general_message'}
              ];
          },
          add_new_tag : function(){
              this.journal_tags.push({tag:this.new_tag});
              for(var i=0;i&lt;this.journal_tags.length;i++){
                  console.log(i + this.journal_tags[i].tag);
              }
              //this.journal_tags.sort();
          }
      });
    })();
    &lt;/script&gt;
  &lt;/dom-module&gt;
  </code></pre>