在Spark列表上使用虚拟布局时滚动

Question

当我关闭virtualLayout时，以下代码正常工作。但是，当我打开virtualLayout时，使用Tab键导航以下列表无法正确滚动。似乎Flex没有意识到新的itemrenrerers可用。想法？

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
    xmlns:s="library://ns.adobe.com/flex/spark" 
    xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955" minHeight="600" creationComplete="firstComponent.setFocus()">

    <s:layout>
        <s:VerticalLayout/>
    </s:layout>

    <s:TextInput id="firstComponent"/>

    <s:List id="lst" hasFocusableChildren="true">
        <s:layout>
            <s:TileLayout requestedColumnCount="3" requestedRowCount="2"/>
        </s:layout>
        <s:itemRenderer>
            <fx:Component>
                <s:ItemRenderer focusIn="itemrenderer1_focusInHandler(event)">
                    <s:states>
                        <s:State name="normal"/>
                        <s:State name="selected" enterState="txt.setFocus();"/>
                    </s:states>
                    <s:layout>
                        <s:VerticalLayout paddingBottom="10" paddingLeft="10" paddingRight="10" paddingTop="10"/>
                    </s:layout>

                    <fx:Script>
                        <![CDATA[
                            import mx.effects.AnimateProperty;

                            import spark.components.DataGroup;
                            import spark.components.List;

                            protected function itemrenderer1_focusInHandler(event:FocusEvent):void
                            {
                                var lst:List = List(owner);
                                var idx:Number = lst.dataProvider.getItemIndex(data);
                                lst.selectedItem = data;

                                // Make sure that the next item is visible
                                idx++;
                                if (idx < lst.dataProvider.length - 1)
                                    lst.ensureIndexIsVisible(idx);  
                            }

                        ]]>
                    </fx:Script>

                    <s:Label text="Renderer"/>
                    <s:TextArea id="txt" text="@{data.text}"/>
                </s:ItemRenderer>
            </fx:Component>
        </s:itemRenderer>
        <s:dataProvider>
            <s:ArrayCollection>
                <fx:Object text="1"/>
                <fx:Object text="2"/>
                <fx:Object text="3"/>
                <fx:Object text="4"/>
                <fx:Object text="5"/>
                <fx:Object text="6"/>
                <fx:Object text="7"/>
                <fx:Object text="8"/>
                <fx:Object text="9"/>
                <fx:Object text="10"/>
                <fx:Object text="11"/>
                <fx:Object text="12"/>
                <fx:Object text="13"/>
                <fx:Object text="14"/>
                <fx:Object text="15"/>
                    </s:ArrayCollection>
        </s:dataProvider>
    </s:List>

</s:Application>