title: Tinymce paste_preprocess unexpected behaviour
body: <p>In tinymce editor I have the following function while pasting some content.</p>
  
  <pre><code>$mceInit['paste_preprocess'] = "function(plugin, o) {
              o.content = '&lt;div class=\"pasted_content\"&gt;'+o.content+'&lt;/div&gt;';
          }";
  </code></pre>
  
  <p>After adding this, when I paste some content it is working as expected.</p>
  
  <pre><code>&lt;div class="pasted_content"&gt;whatever content I pasted&lt;/div&gt;
  </code></pre>
  
  <p>But the problem is whatever I type in the editor after the paste process is also having the above div appended to it. How to solve this issue?</p>