In Randy Disgrills starter masterpage the body element has scroll="no", why must it have this?
<body scroll=”no” onload=”…” class=”v4master”>
The two important parts of the tag are the “scroll” and “class” attributes. The “scroll” attribute is used to force IE to hide the page scrollbar. Since SharePoint handles the scrollbar independently, we need to stop the browser from interfering. For other browsers, the scrollbar is hidden using CSS styles which are explained later in this post. The CSS class applied to the “body” tag is used to apply CSS styles in the corev4.css stylesheet which are part of the Ribbon posITioning system. If you are using a custom stylesheet, you may leave this out; but make sure to apply the needed CSS styles in some other way (perhaps by referencing “body” directly in your stylesheet).
Source Link MasterPageIssues