✔ display:block macht bei IE Probleme

body {
  background-color:#333333;
  }
  
  div#navigation {
  background-color:#999999;
  width:150px;
  padding:5px;
  font-family:Tahoma, Verdana, Arial, sans-serif;
  font-size:12px;
  margin:0;
  }
  
  ul#hauptmenu {
  padding:0;
  margin:0;
  list-style-type: none;
  display:block;
  }
  
  #hauptmenu li {
  background-color:none;
  padding:0;
  margin:0;
  }
  
  #hauptmenu a {
  background-color:#000000;
  color:#999999;
  padding:5px;
  margin:5px 0 5px 0;
  display:block;
  text-decoration:none;
  border-left:10px #333333 solid;
  }
  
  #hauptmenu a:hover {
  background-color:#ffffff;
  color:#333333;
  text-decoration:none;
  border-left:10px #ff9900 solid;
  }
  
  ul#untermenu {
  list-style-type:none;
  margin:5px 4px 10px 4px;
  padding:0;
  }
  
  #untermenu a {
  color:#333333;
  font-size:11px;
  text-decoration:none;
  background-color:#999999;
  padding:0;
  margin:0;
  display:block;
  border:0;
  }
  
  #untermenu a:hover {
  color:#ffffff;
  font-size:11px;
  text-decoration:none;
  background-color:#999999;
  border:0;
  padding:0;
  margin:0;
  }
  
  #untermenu a .hoverpfeil{
  color:#999999;
  }
  
  #untermenu a:hover .hoverpfeil{
  color:#ff9900;
  }

.... 

<div id="navigation">
  <ul id="hauptmenu">
  <li><a href="#">STARTSEITE</a></li>
    <ul id="untermenu">
    <li>
    <a href="#"><span class="hoverpfeil">»</span> Neuigkeiten</a>
    </li>
    <li>
    <a href="#"><span class="hoverpfeil">»</span> Neuigkeiten-Archiv</a>
    </li>
    <li>
    <a href="#"><span class="hoverpfeil">»</span> Neuigkeiten einsenden</a>
    </li>
    </ul>
  <li><a href="#">MAGAZIN</a></li>
  <li><a href="#">INFO</a></li>
  <li><a href="#">FORUM</a></li>
  <li><a href="#">KONTAKT</a></li>
  </ul>
</div>

<!--[if IE]>
<style type="text/css">
#hauptmenu a {
	width:		100%;
}
</style>
<![endif]-->