[SB65]

No, this is a css issue - that is a suckerfish menu. There are two issues: #color_header is behind #main, and within #color_header .mainmenu is behind #pagetitle. Both of these mean that the drop down menu loses focus on :hover when the mouse moves down, and so the menu disappears.

Have a try making the following amendments to your css (style.php), in red:

#color_header {
    background-color: transparent;
    background-image: none;
    margin-top: -85px;
    max-height: 40px;
    position: relative;
    z-index:3
}

.mainmenu {
    background: none repeat scroll 0 0 transparent;
    height: 3em;
    position: relative;
    z-index: 2;
}

div#pagetitle.clearfix.row {
    background: none repeat scroll 0 0 transparent;
    position: relative;
    z-index: 1;
}

Incidentally, you have a style tag located between your head and body tags. I'd sort that as it may lead to unexpected behaviour.