spark.components.PopUpAnchor - Added/RemovedEffect Does Not Work With spark.effects.Fade and throws RTE

Steps to reproduce:
1. Compile and run the pasted app.
2. Click the "Open" button.
3. Click the "Close" button.

Actual Results:
Error: addChildAt() is not available in this class. Instead, use addElementAt() or modify the skin, if you have one.
at spark.components::Group/addChildAt()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\Group.as:1802]
at mx.effects::EffectManager$/removedEffectHandler()[E:\dev\trunk\frameworks\projects\framework\src\mx\effects\EffectManager.as:796]
at Function/http://adobe.com/AS3/2006/builtin::apply()
at mx.core::UIComponent/callLaterDispatcher2()[E:\dev\trunk\frameworks\projects\framework\src\mx\core\UIComponent.as:10873]
at mx.core::UIComponent/callLaterDispatcher()[E:\dev\trunk\frameworks\projects\framework\src\mx\core\UIComponent.as:10811]

Expected Results:
The popUpAnchor fades out.

APP:
<?xml version="1.0" encoding="utf-8"?>
<s:Application
xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:mx="http://ns.adobe.com/mxml/2006"
xmlns:s="library://ns.adobe.com/flex/spark">

<s:states>
<s:State name="closed" />
<s:State name="open" />
</s:states>

<fx:Declarations>
<s:Fade id="fade"/>
</fx:Declarations>

<s:Group top="10" horizontalCenter="0">
<s:Button id="openBtn" label="OPEN" click="currentState = 'open'"/>

<s:PopUpAnchor id="formPUA" left="0" bottom="0" popUpPosition="below" height="21" width="70"
includeIn="open"
displayPopUp.closed="false" displayPopUp.open="true"
addedEffect="

">

<s:Border borderWeight="5">
<s:Label text="Hello World" verticalCenter="0" horizontalCenter="0"/>
<s:Button bottom="5" left="5" right="5" label="CLOSE" click="currentState = 'closed'"/>
</s:Border>

</s:PopUpAnchor>
</s:Group>

</s:Application>