Auto Height Control animation problem

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Silverlight

animation

Hi!
I'm trying to animate the height property of a control, to resize it at the press of a button (working on the property with a DoubleAnimation). If I initialize the height property to a defined value (in the XAML), the animation works well. But I if initialize the height property to Auto (in the XAML; I'd have it so to have the size of the control vary dynamically based on its content), the animation doesn't work (it starts, but it produces no effect).
Anyone knows if there's a method to animate a property initialized to "Auto"?