Did you make any modifications to the home menu manually? It looks like the structure of the menu on the page is causing this issue. The correct structure of the menu should be something like this:
<ul class="level-0" id="cssmw0">
<li class="parent"><a href="#">Item 1</a>
<ul class="level-1">
<li><a href="#">Sub Item 1</a></li>
<li><a href="#">Sub Item 2</a></li>
<li><a href="#">Sub Item 3</a></li>
</ul>
</li>
<li><a href="#">Item 2</a></li>
<li><a href="#">Item 3</a></li>
</ul>
From what I could tell, there are a lot of extra ul and li tags in your menu.