If AllowPaging, AllowScroll and UseStaticHeaders are set to true, then there will be 2 empty <th> elements

workaround: 
    <ClientSettings>
...
        <ClientEvents OnGridCreated="OnGridCreated" />
    </ClientSettings>

<script>
    function OnGridCreated(sender, args) {
        var emptyth = $telerik.$(sender.get_element())
            .find("th").filter(function (ind, item) { return item.textContent == "" });
        // alert(emptyth.length)
        emptyth.append("<span style='display:none'>Hidden empty table header</span>")
    }
</script>