I too can verify this problem exists with the code Ryan. The outputted code looks like the following for me.
html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd"><html><body><p>This is a <strong>markdown</strong> enabled text</p><divclass="highlight"><pre><spanclass="nb">puts</span><spanclass="s2">"Hello World"</span></pre></div></body></html>
I too can verify this problem exists with the code Ryan. The outputted code looks like the following for me.
Using Nokogiri 1.4.6