I'm uncertain how to aptly describe my question: It's a bug, that just needs debugging.

Here's my jsFiddle: http://jsfiddle.net/Wagtail/b6Juh/18/

I need to be able to scroll over Item A, Item B, and Item C instead of just having disappear entirely when my mouse leaves Item A. Why is this happening anyway?

Here's the JavaScript, HTML, and CSS codes copied over for your convenience:

HTML Code:
<table id="headMenu">
        <td id="head1">Item 1</td>
        <td id="head2">Item 2</td>
        <td id="head3">Item 3</td>
<table id="subMenu">
        <td>Dynamic Content!</td>
CSS Code:
#headMenu{background:rgb(142,180,227);width:90%;height:50px;color:white;font-weight:bold;text-align:center;margin:20px 5%  0px 5%%;vertical-align:middle;}
#subMenu{background:rgb(195,214,155);width:90%;height:50px;color:white;font-weight:bold;text-align:center;margin:1px 5% auto 5%;vertical-align:middle;}
#headMenu td:hover{background:rgb(162,200,240);}
#subMenu td:hover{background:rgb(210,230,170);}​
JavaScript Code:
var a = 500, head1 = document.getElementById('head1'), subMenu = document.getElementById('subMenu'), timeout;

head1.onmouseover = function(displayMenu) {
    subMenu.innerHTML = '<tr><td>Item A</td><td>Item B</td><td>Item C</td></tr>';
    head1.onmouseout = function(getScroll) {
        subMenu.onmouseover = function(breakTimeout) {
            subMenu.onmouseout = function(endFunction) {
                subMenu.innerHTML = '<tr><td>Dynamic Content!</td></tr>';
        timeout = setTimeout(function() {
            document.getElementById("subMenu").innerHTML = '<tr><td>Dynamic Content!</td></tr>';
        }, a);
Thanks in advance to any answers! If you need clarification, I'll be happy to reply.