I answered this question (links to my answer) and uploaded a couple of screenshots:
When I was composing the answer one of the uploaded screenshots wouldn't appear in the preview properly:
Yi on chat had a look and it noted that removing the
<pre> tags resolves this and that
showdown.js (?) might not be handling raw HTML markup properly?
Arjan also points out in his answer that using sole
<-- without a corresponding inside the
<pre></pre> tags is also breaking something. See below.