Bootstrap panels displayed with 0 margin-bottom

Problem/Motivation

In converting a client to DrupalWxT we have found that bootstrap panels are displayed without any space in between - see image. It occurs specifically if the upper panel is wrapped in a div which triggers the following CSS in wxt_bootstrap style.css that removes the bottom margin:

p:last-child,
.form-group:last-child,
.panel:last-child {
  margin-bottom: 0; }

Steps to reproduce

To reproduce:

1. Paste the following markup into the WYSIWYG source editor:

<div class="my-class">
<section class="panel panel-default well"><header class="panel-heading"><h3 class="panel-title">Example</h3>
</header><div class="panel-body">
<p>Panel 1 text</p>
</div>
</section>
</div>
<section class="panel panel-default"><header class="panel-heading"><h3 class="panel-title">Note</h3>
</header><div class="panel-body">
<p>Panel 2 text</p>
</div>
</section>

2. Save the node and the problem will be seen on node view.

Proposed resolution

I am not sure the reason for this code, so I am unsure whether it should be removed or re-targeted, so I am unsure of how to fix the problem.