Second CSS class not working in IE8

Question

I have the following div to be passed to the client, but in IE the class is checked-yesignored. If I look at the target element in the Developer Tools, this class is completely missing in the Style panel. The class shift-item-presentis connected to the server, and the client side of the class checked-yes, depending on the attribute of the presentparent row, is also shown below.

<td><div class="shift-item-present checked-yes" jQuery1272958392665="94"/></td>

Parent line:

<tr class="shift-item" id="ctl00_mainContentPlaceHolder_ctl00_shiftList_ctl01_shiftRow" present="True" shift-id="641" jQuery1272958392665="64">

The page works fine in FF. Here is the CSS, both in the same file:

.shift-item-present
{
    top: 2px;
    left: 2px;
    height: 12px;
    width: 20px;
    background-repeat: no-repeat;
    background-position: center right;
}

.checked-yes
{
    background-image: url('../Images/Icons/checked-yes-xs.png');
}

Answer 1

Internet Explorer XHTML! IE8. , . <div></div> <div/>.

Answer 2

, IE8 Quirks. DOCTYPE.