BarChart won't show Slide Effect

Question

I've defined a BarChart and a SeriesSlide Effect in the mxml.
I am programatically populating the BarChart using web services and
I set the dataprovider of the BarChart in the webservice handler.
The data gets refreshed and the chart updates instantaneously
without the sliding effect.
I've linked the slide effect in the BarSeries like so:
<mx:BarSeries .... showDataEffect="{slideIn}" ....
/>

Answer 1

Script side:
[Bindable]
public var m_barDataProvider:XMLList;
private function treeNodeItemHandler(event:ResultEvent):void
var result_xml:XML = CleanXML(event.result);
barchart0.height = result_xml.child("node").length() * 22;
m_barDataProvider = result_xml.children();
<mx:WebService
id="wsKX"
wsdl="
http://betterthinkfast/KX_WS/Service.asmx?wsdl"
useProxy="false" showBusyCursor="true"
>
<mx:operation name="GetOtherL2ForL2Docs"
result="treeNodeItemHandler(event)"/>
</mx:WebService>
<mx:SeriesSlide id="slideIn" duration="1000"
direction="right"/>
<mx:BarChart id="barchart0" showDataTips="true"
height="100%" width="100%"
dataProvider="{m_barDataProvider}"
itemClick="BarClickHandler(event)" >
<mx:verticalAxis>
<mx:CategoryAxis categoryField="@label"/>
</mx:verticalAxis>
<mx:series >
<mx:BarSeries yField="@label" xField="@count"
displayName="Documents" showDataEffect="{slideIn}"/>
</mx:series>
</mx:BarChart>
am I missing anything?
Thanks Masamune