SL2B1 - High CPU usage with ListBox and animation in same app. Why?

Hi,

I have a simple app made from a 2-cell grid.  One cell contains a ListBox the other a slow-moving animation.  The app uses hardly any CPU when the animation is running and the ListBox is empty.  But when 1000 strings are added to the ListBox the app uses over 40% of my CPU.  There is no visual overlap between the ListBox and the animation.  So why should the ListBox have any interaction with the animation and use so much CPU?  

I have a write-up, demo app and source code here: www.alancobb.com/pub/SL2/SL2B1_Bugs/ListBoxInteractionWithAnimationPerfIssue/ProblemDescription.htm

Any explanations? Work-arounds?

Thanks,
Alan Cobb
www.alancobb.com/blog (Silverlight blog)
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