V 1.0 Visibility Property Breaking Change
In order to reduce surface area, we removed Visibility.Hidden from the product. Prior to this change Visibility.Hidden behaved the same as Visibility.Collapsed. From a functionality stand-point, the Silverlight behavior is closer to the WPF Visibility.Collapsed so we've decided to keep Collapsed. To create content that will work consistently between Mix and 1.0, replace all occurrences of “Hidden” in both XAML and script with “Collapsed”.
sender.findName("fsm").visibility = "Hidden";
Needs to be changed to:
sender.findName("fsm").visibility = "Collapsed";
And for XAML, replace:
<Canvas x:Name="mask" Visibility="Hidden">
<Canvas x:Name="mask" Visibility="Collapsed">