Hi DaveE,
there is a small, but ugly, HTML error in your default widget template in /views/widget.php
You have the echo $after_widget; statement within your if( $flexible_posts->have_posts() ) conditional, so by default a closing </div> is missing and messes up the sidebar output.
Before
[...]
</ul><!-- .dpe-flexible-posts -->
<?php
echo $after_widget;
else: ?>
<div class="no-posts dpe-flexible-posts">
<p>No post found</p>
</div>
<?php
endif; // End have_posts()
?>
After
[...]
</ul><!-- .dpe-flexible-posts -->
<?php else: ?>
<div class="no-posts dpe-flexible-posts">
<p>No post found</p>
</div>
<?php
echo $after_widget;
endif; // End have_posts()
?>
I mentioned it while fetching a taxonomy with no posts in.