IE not breaking out of <div> to display border?

[tawxic]

My code is thus:
<div id="navigation" >
<ul>
<li><a href="#">Home</a></li>
<li><a href="#">About Phazm</a></li>
<li><a href="#">Servic es Offered</a></li>
<li><a href="#">Reques t Services</a></li>
<li><a href="#">CEO Blog</a></li>
<li><a href="#">Contac t</a></li>
</ul>
</div>

style:
#navigation {
background-color:#94cc5d;
height:1.2em;
}

#navigation a {
color:#121212;
}

#navigation a:hover {
color:#5F5F5F;
border-bottom:thick solid #94cc5d;
}
#navigation ul li {
display:inline;
padding-right:1.2em;
}
In FF, this works great, but IE is stopping the border-bottom from
showing, due to the encapsulating div tag.