The animation value is just another value source, in fact the animation value is not modifying the local value (that remains the same during all the animation duration). You can specify how your storyboard behaves when the animation completes by setting the FillBehavior property:

• <Storyboard x:Key="anim"> or <Storyboard x:Key="anim" FillBehavior="HoldEnd"> is the default behavior, that will maintain the last animated value after animation ends.
• <Storyboard x:Key="anim" FillBehavior="Stop"> will remove last animated value after animation ends, so the local (or any other value with less precedence) will be recovered.