Roy, the third result introduces an odd span tag and looks like this:
<h3 class="posttitle"><a href="http://www.gangleri.nl/bookreviews/261/lull-bruno-frances-amelia-yates-isbn-0710009526/" rel="bookmark" title="Lull & Bruno * Frances Amelia <span class="search-everything-highlight" style="">Yates</span> (isbn 0710009526)">Lull & Bruno * Frances Amelia <span class="search-everything-highlight" style="">Yates</span> (isbn 0710009526)</a></h3>
There are two possibilities I can think of, either your theme is trying to highlight the word "yates", in which case you can edit the search.php to fix that or you're using a plugin which is trying to improve the search results and inserting the "search-everything-highlight" class into your results.
What I can tell you with certainty is that it does not show up on my site, when I search for anything and is not part of the core package. http://www.thisismyurl.com/?s=wordpress