[flexcoders] Transition only works once

[jimmy5804]

I don't use transitions often, so I may be missing something. The transition 
works fine the first time, but the resize is applied instantaneously afterwards.

This is part of a VBox-based MXML component.

Transition is very simple:

<mx:transitions>
        <mx:Transition fromState="" toState="filterView">
                <mx:Resize duration="500" target="{bottomBox}"/>
        </mx:Transition>
</mx:transitions>

The state to which it is applied adds an HBox with several buttons to the the 
parent VBox.

<mx:states>
<mx:State id="filterState" name="filterView">
        <mx:AddChild relativeTo="{topBox}" position="after">
                <mx:target>
                        <mx:Spacer id="vSpacer" height="2"/>
                </mx:target>
        </mx:AddChild>
        <mx:AddChild relativeTo="{this}" position="lastChild">
                <mx:target>
                        <mx:HBox id="bottomBox" width="100%">
                                <!-- Several children here-->
                        </mx:HBox>
                </mx:target>
        </mx:AddChild>
</mx:State>
</mx:states>

Have I done anything particularly dumb here? If not, where should I look to 
start debugging?

TIA,