SparkDataContainer Scroller not scrolling to bottom of container

Question

I am using a scroller component within a custom skin for a SkinnableDataContainer. I am running into an issue in that the thumbbar of the scroller stops at about the 50% point, however this is actually the end of the scrollable area. In actuality, the thumbbar should be at the bottom of the scroll track. Here's the code for the scroller:

<s:SparkSkin xmlns:fx="http://ns.adobe.com/mxml/2009"
         xmlns:s="library://ns.adobe.com/flex/spark"
         xmlns:mx="library://ns.adobe.com/flex/halo" bottom="150"  >

<!-- Properties of the parent ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->

<s:states>
    <s:State name="normal" />
    <s:State name="disabled" />
</s:states> 


<!-- Metadata ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->   

<fx:Metadata>
    [HostComponent("spark.components.SkinnableDataContainer")]
</fx:Metadata>  


<!-- UI components ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->

<s:Rect left="0" right="0" 
        bottom="0" top="0"
        radiusX="4" radiusY="4"   >
    <s:fill>
        <s:SolidColor id="fillColor" color="0xEFEFEF"/>
    </s:fill>
</s:Rect>   

<s:Group width="905" height="395" id="mainGroup">
    <s:Scroller left="10" right="10" top="4" bottom="10" >
            <s:DataGroup id="dataGroup" />              

    </s:Scroller>
    <s:Rect left="0" right="0" top="0" bottom="0">
        <s:stroke>
            <s:SolidColorStroke weight="1" color="0xD8D8D8"/>
        </s:stroke>
    </s:Rect>
</s:Group>