$(this).addClass() not working

I can do $(this).children("a").addClass("class") and it works fine, but when I do $(this).addClass("class") it is not working. I am using $(this) within a mouseover function.

$("#site nav li.hasChild").mouseover(function ()
{
    $(this).children("a").addClass("selectedTab");  // works fine
    $(this).addClass("selectedFixTab"); // does not work
    $(this).children("ul").css("display", "block");
});

HTML:

<header id="site">
    <nav>
        <ul>
            <li id="Li1" class="hasChild">
                <a href="#">Fix</a>
                <ul>
                    <li><a href="#">1</a></li>
                    <li><a href="#">2</a></li>
                    <li><a href="#">3</a></li>
                    <li><a href="#">4</a></li>
                    <li><a href="#">5</a></li>
                </ul>
            </li>
            <li id="Li2" class="hasChild">
                <a href="#">Learn</a>
                <ul>
                    <li><a href="#">1</a></li>
                    <li><a href="#">2</a></li>
                    <li><a href="#">3</a></li>
                    <li><a href="#">4&开发者_如何学Clt;/a></li>
                </ul>
            </li>
            <li id="Li3">
                <a href="contact.htm">Contact</a>
            </li>
        </ul>
    </nav>
</header>

CSS:

.selectedFixTab
{
    border-top:1px solid #eb7c00;
    border-left:1px solid #eb7c00;
    border-right:1px solid #eb7c00;
}

.selectedLearnTab
{
    border-top:1px solid #2d70a3;
    border-left:1px solid #2d70a3;
    border-right:1px solid #2d70a3;
}

.selectedTab
{
    border-bottom:1px solid #fff;
}

It successfully adds the "selectedFixTab" class to the top level LI tags as soon as the mouse hovers over the LI tag. You can see it in action here in this jsFiddle: http://jsfiddle.net/jfriend00/mj2u6/.

I'm not sure it's doing exactly what you intend, but it is doing what the code says to do. If you care to explain what you're trying to accomplish, we can likely help you fix the code to do what you want.

$("#site nav li a").mouseover(function ()
{
    $(this).children("a").addClass("selectedTab");  // works fine
    $(this).addClass("selectedFixTab"); // does not work
    $(this).children("ul").css("display", "block");
});

I think this is what you want it to do!