Why does a floated <input> control in a floated element slide over too far to the right in IE7, but not in Firefox?

<fieldset id="RequestInformation">
   <legend>Request Information</legend>
   <ol>
     <li>
       <label id="ctl00_ContentPlaceHolder1_txtRequestDate_L" class="stdLabel"
         for="ctl00_ContentPlaceHolder1_txtRequestDate">Request Date:</label>
       <div class="FormGroup">
         <input id="ctl00_ContentPlaceHolder1_txtRequestDate" class="RSV DateTextBox hasDatepicker"
           type="text" value="10/05/2004" name="ctl00$ContentPlaceHolder1$txtRequestDate"/>
         <img class="ui-datepicker-trigger" src="/PROJECT/images/Calendar_scheduleHS.png" alt="..." title="..."/>
         <span id="txtRequestDate_error"/>
       </div>
     </li>
     --STUFF DELETED HERE--
     <li>
       <label id="ctl00_ContentPlaceHolder1_chkAppealed_L" class="stdLabel"
         for="ctl00_ContentPlaceHolder1_chkAppealed"> Request Appealed?</label>
       <div class="FormGroup">
         <span class="stdCheckBox">
           <input id="ctl00_ContentPlaceHolder1_chkAppealed" type="checkbox" name="ctl00$ContentPlaceHolder1$chkAppealed"/>
         </span>
       </div>
     </li>
   </ol>
 </fieldset>

div
{
    border-style: solid;
    border-width: thin;
    border-color:Orange;
}

label
{
    border-style: solid;
    border-width: thin;
    border-color:Blue;
}

.FormGroup
{
    float:left;
    margin-left: 1em;
    clear: right;
    width: 75em;
}

.FormGroup > *
{
    float:left;
    background-color: Yellow;
}

fieldset ol
{
    list-style: none;
}

fieldset li
{
    padding-bottom: 0.5em;
}

li > label:first-child
{
    display: block;
    float: left;
    width: 10em;
    clear: left;
    margin-bottom: 0.5em;
}

em
{
    color: Red;
    font-weight: bold;
}

//IE Margin fix:
//  http://www.positioniseverything.net/explorer/inherited_margin.html
jQuery.each(jQuery.browser, function(i) {
    if($.browser.msie){
        $(":input").wrap("<span></span>");
    }
});