[jQuery] Superfish - Tabbing through menu when it's a nested ul causes the menu to disappear

[Jeremy]

I'm testing the accessibility of the Superfish menu by tabbing through
it.  My setup is such that the sf-menu is nested within an li of
another ul.  The first time tabbing through, everything works as
expected.  But, once you've tabbed away from the last item in the
menu, the menu disappears.  Here's the basic html I'm using.  Any
suggestions?

<ul>
    <li>Sample Item 1</li>
    <li>
        <ul class="sf-menu">
            <li><a href="#">Menu Item 1</a>
            </li>
            <li><a href="#">Menu Item 2</a>
            </li>
        </ul>
    </li>
</ul>