Seems like an issue with all the percentage widths. I know WebKit can have issues with nested and rounded percentages etc, so when the page is resized both the widths on the images and quotes, as well as padding on the parent element are recalculated.
You'll see if you remove the padding: 0 5%
on the max-width
class, the problem no longer occurs.
Try wrapping the quotes in a 100% width div:
<div class="quote-wrapper" style="width: 100%;">
<div class="reference clear-both">
<img src="images/monica.jpg" alt="Monica" class="reference-pic">
</div>
<div class="quote">
<p><em>“Paul is the most committed hard working person I've had the pleasure to supervise. If he was unfamiliar with something he did the research to inform himself and others. Paul is one of those rare breed of people who comes to a supervisor with options not just problems.”</em></p>
<p>Monica Luchak, Former Director of Creative Services, BoardSource</p>
</div>
</div>