title: Button shifting on mouse hover
body: <p>I've got a problem with my menu buttons shifting whenever I'm hovering over them with my mouse. Once I've done that they're all in place. When I press F5 to relaod the page the buttons are already in place. The problem does not occur in IE8. I'm using Chrome (updated).</p>
  
  <p>CSS:</p>
  
  <pre><code>div.header_container
  {
      clear: both;
      float: left;
      height: 180px;
      width: 100%;
  }
  
  div.header
  {
      margin-top: 54px;
      height: 110px;
      background-color: #000000;
      width: 100%;
  }
  
  div.logo
  {
      float: left;
      margin-top: 23px;
      margin-left: 5px;
  }
  
  div.menu
  {
      float: right;
      margin-top: 58px;
      margin-right: 10px;
  }
  
  div.menu ul
  {
  
  }
  
  div.menu ul li
  {
      float: left;
      margin-left: 30px;
      padding-right: 10px;
      list-style-image:url("../images/menu_block.jpg");
  }
  
  div.menu ul li:hover
  {
      list-style-image:url("../images/menu_block_mo.png");
  }
  
  div.menu ul li a
  {
      text-decoration: none;
      color: #ffffff;
      font-size: 16px;
      font-family: 'CalibriRegular';
  }
  </code></pre>
  
  <p>HTML:</p>
  
  <pre><code>        &lt;div class="wrapper"&gt;
      &lt;div class="header_container"&gt;
          &lt;div class="header"&gt;
              &lt;div class="logo"&gt;
                  &lt;a href="#" title="Video Photo Editing Graphics | Stefanvlemmix.nl"&gt;&lt;img src="images/logo.png" /&gt;&lt;/a&gt;
              &lt;/div&gt;
              &lt;div class="menu"&gt;
                  &lt;ul&gt;
                      &lt;li&gt;&lt;a href="./index.html"&gt;Start&lt;/a&gt;&lt;/li&gt;
                      &lt;li&gt;&lt;a href="#"&gt;About&lt;/a&gt;&lt;/li&gt;
                      &lt;li&gt;&lt;a href="./projects.html"&gt;Projects&lt;/a&gt;&lt;/li&gt;
                      &lt;li&gt;&lt;a href="#"&gt;Contact&lt;/a&gt;&lt;/li&gt;
                  &lt;/ul&gt;
              &lt;/div&gt;
          &lt;/div&gt;
      &lt;/div&gt;
      &lt;/div&gt;
  </code></pre>
  
  <p>Any idea what I'm doing wrong?</p>