title: JS select2 plugin not scrolling when options are open
body: <p>I am using JS Select2 library to use as multiple options select. The select is positioned within a <code>div</code> which is scrolled by its parent <code>div</code> with <code>css</code> - <code>overflow-y: scroll</code>. The nested <code>div</code> scrolls fine until an option is opened. When options are opened then the <code>div</code> becomes un-scrollable <em>unless</em> it is scrolled on the select options. Not sure if the source of the problem is my html/css or its the <code>select2</code> lib. </p>
  
  <p>Thanks in advance for any help!</p>
  
  <p>My markup:</p>
  
  <pre><code>&lt;div id="topcontainer" style="padding-top: 100px; overflow-y: scroll;  position: absolute; height: 1000px; width: 500px; background: #6d3353"&gt;
  &lt;div id="parent" style="position: relative; height: 3000px; width: 200px; background: #e4b9b9"&gt;
      &lt;select class="js-example-basic-multiple" name="states[]" multiple="multiple"&gt;
          &lt;option value="AL"&gt;aaaaaaa&lt;/option&gt;
          &lt;option value="AL"&gt;bbbbbbb&lt;/option&gt;
          &lt;option value="AL"&gt;ccccccc&lt;/option&gt;
          &lt;option value="WY"&gt;ddddddd&lt;/option&gt;
      &lt;/select&gt;
      &lt;script&gt;
  
          $(document).ready(function () {
              $('.js-example-basic-multiple').select2();
          });
      &lt;/script&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>
  </p>