It looks like MoveDirection.TopIn causes the window to slide up from the bottom, and MoveDirection.BottomIn causes the window to slide down from the top. LeftIn and RightIn are correct (window slides in from the left or right, respectively). All of the Outs are correct. So it's only TopIn and BottomIn that are reversed.
Duration duration = new Duration(TimeSpan.FromMilliseconds(250));
SettingsWindow.OpenAnimation = new RadSlideAnimation()
FillBehavior = AnimationFillBehavior.Stop,
Duration = duration,
MoveDirection = MoveDirection.TopIn