Bootstrap accordion panel-body not collapsing on first hit

I have the following accordion defined which otherwise works fine, except that the first panel-body does not collapse after expanding the second panel-body, though it does eventually collapse if I click the Second headline for a second time.

I can work around the problem by using "panel-collapse collapse" instead of "panel-collapse collapse in" for the first headline, however I would like to avoid having to do this as this reduces the usability of the page.

Any advise of what may be causing this anomaly?

<!-- language: lang-html -->

{% extends "base.html" %}
{% import "bootstrap/wtf.html" as wtf %}

<div class="page-header">
    <link href="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/css/bootstrap.css" rel="stylesheet"/>
    <script src="//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.js"></script>
    <script src="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/js/bootstrap.js"></script>
</div>

<div class="panel-group" id="accordion" role="tablist" aria-multiselectable="true"><div class="panel panel-default">
    <div class="panel-heading" role="tab" id="headingOne">
      <h4 class="panel-title">
        <a data-toggle="collapse" data-parent="#accordion" href="#collapseOne" aria-expanded="true" aria-controls="collapseOne">
          1. Headline One
        </a>
      </h4>
    </div>
    <div id="collapseOne" class="panel-collapse collapse in" role="tabpanel" aria-labelledby="headingOne">
      <div class="panel-body">
            Some text
      </div>
    </div>
  </div>
  <div class="panel panel-default">
    <div class="panel-heading" role="tab" id="headingTwo">
      <h4 class="panel-title">
        <a class="collapsed" data-toggle="collapse" data-parent="#accordion" href="#collapseTwo" aria-expanded="false" aria-controls="collapseTwo">
          2. Second headline
        </a>
      </h4>
    </div>
    <div id="collapseTwo" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingTwo">
      <div class="panel-body">
          Some more text
      </div>
    </div>
  </div>
</div>

Check the version of Bootstrap that you're using. It appears to be working here for v3.3.2

<!-- begin snippet: js hide: false --> <!-- language: lang-html -->

<link href="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/css/bootstrap.css" rel="stylesheet"/>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/js/bootstrap.js"></script>

<div class="panel-group" id="accordion" role="tablist" aria-multiselectable="true">
  
  <div class="panel panel-default">
    <div class="panel-heading" role="tab" id="headingOne">
      <h4 class="panel-title">
        <a data-toggle="collapse" data-parent="#accordion" href="#collapseOne" aria-expanded="true" aria-controls="collapseOne">
          1. Headline One
        </a>
      </h4>
    </div>
    <div id="collapseOne" class="panel-collapse collapse in" role="tabpanel" aria-labelledby="headingOne">
      <div class="panel-body">
            Some text
      </div>
    </div>
  </div>
  
  <div class="panel panel-default">
    <div class="panel-heading" role="tab" id="headingTwo">
      <h4 class="panel-title">
        <a class="collapsed" data-toggle="collapse" data-parent="#accordion" href="#collapseTwo" aria-expanded="false" aria-controls="collapseTwo">
          2. Second headline
        </a>
      </h4>
    </div>
    <div id="collapseTwo" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingTwo">
      <div class="panel-body">
          Some more text
      </div>
    </div>
  </div>

</div>

<!-- end snippet -->