I think this has to be a bug of some kind. As a test I took an example from Adobe's livedocs site and changed a vbox for a panel.
The transitions work with the vbox but not with a panel??? <?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute"> <mx:transitions> <mx:Transition id="myTransition" fromState="*" toState="Advanced"> <mx:Parallel target="{panel2}"> <mx:WipeDown duration="2000"/> <mx:Dissolve alphaFrom="0.0" alphaTo="1.0" duration="2000"/> </mx:Parallel> </mx:Transition> <mx:Transition id="backwards" fromState="Advanced" toState="*"> <mx:Sequence targets="{[cb1, cb2, cb3, text1, panel2]}"> <mx:Parallel> <mx:WipeDown showTarget="false" duration="2000" target="{panel2}"/> <mx:Dissolve alphaFrom="1.0" alphaTo="0.0" duration="2000" target="{panel2}"/> </mx:Parallel> <mx:RemoveChildAction/> </mx:Sequence> </mx:Transition> </mx:transitions> <mx:states> <mx:State name="Advanced"> <mx:SetEventHandler target="{linkbutton1}" name="click" handler="currentState=''"/> <mx:AddChild relativeTo="{panel1}" position="lastChild"> <mx:Panel x="10" y="150" width="260" height="151" layout="vertical" title="Test Title" id="panel2"> <mx:CheckBox id="cb1" label="Regular expression"/> <mx:CheckBox id="cb2" label="Case sensitive"/> <mx:CheckBox id="cb3" label="Exact phrase"/> <mx:Text text="Text" textAlign="center" width="100%" id="text1"/> </mx:Panel> </mx:AddChild> </mx:State> </mx:states> <mx:Panel id="panel1" x="5" y="5" width="300" height="400" layout="absolute"> <mx:Label x="20" y="70" text="Search"/> <mx:TextInput x="20" y="90"/> <mx:Button x="185" y="90" label="Go"/> <mx:LinkButton x="20" y="120" label="Advanced Options" click="currentState='Advanced'" id="linkbutton1"/> </mx:Panel> </mx:Application>