title: iPhone shows element with Bootstrap hidden-xs class
body: <p>I have an element on my site with the <code>hidden-xs</code> class on it. When I load it on my iPhone, the element still shows up.</p>
  
  <p>On <a href="http://www.slacre.com" rel="nofollow" title="Slacre.com">Slacre.com</a>, the cover photo has <code>hidden-xs</code> applied to it, and the top-nav isn't using its mobile form.</p>
  
  <p>Why is this happening?</p>