He dejado el código así y me sigue ocurriendo lo mismo:
<mx:transitions>
<mx:Transition fromState="*" toState="grid">
<mx:Parallel>
<mx:Resize target="{creationForm}" duration="500"/>
<mx:WipeRight target="{numColumns}" duration="500"/>
</mx:Parallel>
</mx:Transition>
<mx:Transition fromState="grid" toState="*">
<mx:Parallel>
<mx:Resize target="{creationForm}" duration="500"/>
<mx:WipeUp target="{numColumns}" duration="1000"/>
</mx:Parallel>
</mx:Transition>
<mx:Transition fromState="grid" toState="''">
<mx:Parallel>
<mx:Resize target="{creationForm}" duration="500"/>
<mx:WipeUp target="{numColumns}" duration="1000"/>
</mx:Parallel>
</mx:Transition>
</mx:transitions>