title: slideToggle() does not work properly in IE7
body: <p>I am experiencing problems with jQuery SlideToggle in IE7.
  It works properly in IE8, IE9, FF, Chrome, Opera.
  When i debug i don't get any errors. The only thing that's happening is my event.preventDefault() but by some reason IE7 isn't even trying to do anything after my if statement.
  Here is some code:</p>
  
  <pre><code>/* For handling of open/close the toggler button for categories */
  $('ul.categories').on('click', '.toggle button', function(event) {
      event.preventDefault();
      var $categories = $(this).parent().next('.items'),
          $icon = $('.icon', this);
      $categories.slideToggle(Interface.animationDuration, function() {
          //Somewhere here is stops. It does not even slideToggle.
          if ($(this).is(':visible')) {
              $icon.removeClass('white-arrow-down').addClass('white-arrow-up');
          } else {
              $icon.removeClass('white-arrow-up').addClass('white-arrow-down');
          }
      });
  });
  
  &lt;ul class="categories"&gt;
      &lt;li class="toggle"&gt;&lt;button type="button"&gt;&lt;span class="icon white-arrow-down"&gt;&lt;/span&gt;&lt;/button&gt;&lt;/li&gt;
      &lt;ul class="items"&gt;
          &lt;li&gt;
              &lt;input type="radio" name="category" id="" value=""&gt;&lt;label for=""&gt;&lt;/label&gt;
          &lt;/li&gt;
          &lt;li&gt;
          &lt;input type="radio" name="category" id="" value=""&gt;&lt;label for=""&gt;&lt;/label&gt;
          &lt;/li&gt;
      &lt;/ul&gt;
  &lt;/ul&gt;
  </code></pre>