listbox invalidate partial missing to updating listheader

<zk>
    <zscript><![CDATA[
        ListModelList model = new ListModelList();
        int size = model.size();
        public void addModelItem() {
            size++;
            model.add("item-" + size);
            lh.setLabel("" + size);
            lb.setValue("" + size);
        }
    ]]></zscript>
    <div>
        <button label="Add Entry" onClick="addModelItem()"/>
        <label id="lb" value="${size}"/>
        <listbox model="${model}" width="200px">
            <listhead>
                <listheader id="lh" label="${size}"/>
            </listhead>
        </listbox>
    </div>
</zk>