List Scrollbar not appearing

Question

I have a spark list with a data provider property that changes often, if the list only has a few items in it no vertical scrollbar appears as expected.
However when the data provider changes the vertical scrollbar doesn't always appear automatically meaning i cann't view all the items in the list.
Is there anyway to force a scrollbar to display?

Answer 1

I've posted my code below for my Item renderer. Tried setting a minwidth and min height but that didn't work.
It happens when the dataProvider only has a few items in which doesn't need a scrollbar. If i quickly change to another dataProvider that does need a scrollbar, the problem occurs and a scrollbar does not appear.
It also happens in reverse. If a dataprovider is chosen that needs a scrollbar, one appears. But then if i quickly change to a dataprovider that doesn't need a scrollbar, the previous scrollbar is still there, until i try to click it, then it disappears.
<?xml version="1.0" encoding="utf-8"?>
<s:ItemRenderer xmlns:fx="http://ns.adobe.com/mxml/2009"
                    xmlns:s="library://ns.adobe.com/flex/spark"
                    xmlns:mx="library://ns.adobe.com/flex/mx"
                    autoDrawBackground="false" width="300" height="300" xmlns:local="*">
     <s:states>
          <s:State name="normal"/>
          <s:State name="selected"/>
     </s:states>
     <s:BorderContainer borderVisible="true" borderColor="black" width="100%" height="100%" borderStyle="solid" left="5" right="5" top="5" bottom="5">
          <s:CheckBox id="checkbox" selected.normal="false"
                    selected.selected="true"/>
          <mx:Image id="thumb" horizontalCenter="0" verticalCenter="0" source="{'http://someserver.com/folderA'+data.filePath+data.fileName+'.png'}"/>
     </s:BorderContainer>
     <fx:Script>
          <![CDATA[
               import flashx.textLayout.factory.TruncationOptions;
               import mx.events.FlexEvent;
               import mx.events.ItemClickEvent;
               protected function thumb_clickHandler(event:MouseEvent):void
                    var ev:ItemClickEvent = new ItemClickEvent(ItemClickEvent.ITEM_CLICK, true);
                    ev.item = data;
                    ev.index = itemIndex;
                    dispatchEvent(ev);
          ]]>
     </fx:Script>
</s:ItemRenderer>