Inline masking not working with percentages

Steps to reproduce:
1. Compile and run this Flex application:

<?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">

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

<s:Group width="100%" height="100%">
<s:Rect width="100%" height="100%">
<s:fill>
<s:SolidColor color="red" />
</s:fill>
</s:Rect>
<s:mask>
<s:Group width="100%" height="100%">
<s:Ellipse width="100%" height="100%">
<s:fill>
<s:SolidColor color="blue" />
</s:fill>
</s:Ellipse>
</s:Group>
</s:mask>
</s:Group>

<!-- workaround: use binding -->

<s:Group id="group2" width="100%" height="100%">
<s:Rect width="100%" height="100%">
<s:fill>
<s:SolidColor color="green" />
</s:fill>
</s:Rect>
<s:mask>
<s:Group width="

" height="

">
<s:Ellipse width="100%" height="100%">
<s:fill>
<s:SolidColor color="blue" />
</s:fill>
</s:Ellipse>
</s:Group>
</s:mask>
</s:Group>

</s:Application>

Actual Results:

A white space then a green circle

Expected Results:

A red circle then a green circle

Workaround (if any):

Use binding to size the mask