listen for the change
event. It will solve your problem.
<s:HGroup>
<s:NumericStepper change="trace('ns change')" value="{ns2.value}" minimum="{ns2.minimum}" maximum="{ns2.maximum}"/>
<s:NumericStepper minimum="0" maximum="1000" id="ns2" />
</s:HGroup>
The change
event gets fired when an input component's value is changed by user interaction. If some part of your code is changing that component's value, the change
event will not get fired.