Átnéztem a style.css almenü részét és sajnos nem igazán jövök rá miért nem gördül le az egér rámutatással:

/* begin MenuSubItem */
.art-menu ul a
{
display:blok;
text-align: center;
white-space: nowrap;
height: 20px;
width: 180px;
overflow:hidden;
line-height: 20px;
margin-right: auto;

background-image: url('images/subitem-bg.png');
background-position: left top;
background-repeat: repeat-x;
border-width: 0px;
border-style: solid;
}

.art-nav ul.art-menu ul span, .art-nav ul.art-menu ul span span
{
display: inline;
float: none;
margin: inherit;
padding: inherit;
background-image: none;
text-align: inherit;
text-decoration: inherit;
}

.art-menu ul a, .art-menu ul a:link, .art-menu ul a:visited, .art-menu ul a:hover, .art-menu ul a:active, .art-nav ul.art-menu ul span, .art-nav ul.art-menu ul span span
{
text-align: left;
text-indent: 12px;
text-decoration: none;
line-height: 20px;
color: #2C3A2D;
font-family: Arial, Helvetica, Sans-Serif;
font-size: 12px;
font-style: normal;
font-weight: normal;
}

.art-menu ul ul a
{
margin-left: auto;
}

.art-menu ul li a:hover
{
color: #FEF5E7;
background-position: 0 -20px;
}

.art-menu ul li:hover>a
{
color: #FEF5E7;
background-position: 0 -20px;
}

.art-nav .art-menu ul li a:hover span, .art-nav .art-menu ul li a:hover span span
{
color: #FEF5E7;
}

.art-nav .art-menu ul li:hover>a span, .art-nav .art-menu ul li:hover>a span span
{
color: #FEF5E7;
}

/* end MenuSubItem */