AJAX :: Hover Menu Position - Contents Are Shown Above Instead Of The Bottom

when I hover over a menu option it's contents are shown above instead of the Bottom off. Even though the hover control says bottom. In my browser and others it works fine, I use IE8. But some browsers it's goes wrong.

<cc1:HoverMenuExtender runat="Server"
TargetControlID="pnlNewCustomers"
PopupControlID="pnlNewCustomerOptions"
HoverCssClass="popupHover"
PopupPosition="Bottom"
OffsetX="10"
OffsetY="-10"
PopDelay="50"
/>
css
.popupHover
{background-image:url(images/header-opened.png);
background-repeat:repeat-x;background-position:left
bottom;
background-color:#F5F7F8;}