You can turn off the Autofill by adding an event:

$FilterAfterChange = <<<FILTERAFTERCHANGE
function (event, status, postData)
{          
    $("input.ui-corner-all.input-elm.hasDatepicker").attr("autocomplete","off");
}
FILTERAFTERCHANGE;
$dg->add_event("jqGridFilterAfterChange", $FilterAfterChange);

$(function(){                  
$("input.ui-widget-content").attr("autocomplete","off");      
});