it's caused by your original Sample.html file having an unclosed <a> tag in it.
Code:
<p class="centered"><span class="centered"><a id="titlebookmark1"><img src="NBCover.jpg" alt="Never Buried Cover" /></span></p>
the reason it has started happening with never versions fo calibre is that the HTML parser has been changed to comply with the HTML 5 spec and that requires unclosed tags like that one to be handled like this. Close the ,a> tag and you will be fine.