jquery UI 1.9 M2 - Menu Bug?

jquery UI 1.9 M2 - Menu Bug?

I just try out the new Menu Feature that comes with latest milestone.

But when I use it, it does not render the background of menu.
The same happens in the jQuery UI Docs Demo of Menu.

http://docs.jquery.com/UI/Menu

When I use

<li><span>menu 1</span></li>

instead of

<li><a href="#"><span>menu 1</span></a></li>

It renders successfully the menu background.

Is this a Bug?

Best Regards

Johannes Geppert

My Blog: http://www.jgeppert.com