No vertical scroll bar on Accordion

I've got a site that uses an Accordion, it has AutoSize="Limit" and the height is set to 600, however, when rendered, the Accordion div style is set to:

"overflow-x: auto; height: 600px; overflow: hidden;"

Does anyone know why this is the case? My understanding is that an AutoSize value of Limit should render style of "overflow-y: auto;" if not "overflow: auto;"?

I tried setting the width to see if that makes any difference, but it still has "overflow: hidden".

At the moment I have a work around which places the Accordion (with AutoSize="None") in a div with a style of "height: 420px; width: 750px; overflow: auto;", but I'm surprised that this issue exists and would prefer if I didn't have to use this work around.

Accordion tag:

<AJAX:Accordion
    ID="LibraryList"
    runat="Server"
    SelectedIndex="-1"
    AutoSize="None"
    FadeTransitions="true"
    TransitionDuration="250"
    FramesPerSecond="40"
    RequireOpenedPane="false"
    HeaderCssClass="IconnedAccordionHeader"
    HeaderSelectedCssClass="IconnedAccordionHeaderSelected"
    ContentCssClass="accordionContent"
    SuppressHeaderPostbacks="true">

Rendered div:

<div id="ctl00_MainBody_LibraryList" style="height:600px;overflow:hidden;overflow-x:auto;">