title: Bootstrap popover (placement: 'top') behaviors incorrect in IE8
body: <p>Here's the javascript code of the pop-over part:</p>
  
  <pre><code>$('#view_case).popover({
      html: true,
      placement: 'top',
      title: 'Test Cases',
      content: function() {
          return $('#case_list').html();
      }
  });
  </code></pre>
  
  <p>And the screenshot of it from IE8:</p>
  
  <p><img src="https://i.stack.imgur.com/CfC8r.png" alt="enter image description here"></p>
  
  <p>There's a small white triangle above the button, which shouldn't be there.</p>
  
  <p>And I noticed <a href="http://twitter.github.io/bootstrap/javascript.html#popovers" rel="nofollow noreferrer">the tutorial page of Bootstrap</a> has the same issue. But when the placement is 'right', it just works fine in IE8.</p>
  
  <p>So is this a common bug? Do we have some workaround for this?</p>