Spark NumericStepper : unable to use decimals as stepSize - Displays NaN

Steps to reproduce:

Simple application with a numeric stepper :

<?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"
xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955" minHeight="600">
<fx:Declarations>
<!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>
<s:NumericStepper maximum="50" stepSize="0.05"/>
</s:Application>

Actual Results:
First click on up arrow is ok (gives 0.05). Next click gives "NaN" and it never changes after.
Manual input of a number with decimals also changes into "NaN"

Expected Results:
Can input or use arrows to decimals number

Workaround (if any):
Compile with 4.1