Fixed final layout problem i'm aware of.

(Currently!)

Perspex.Controls/Primitives/Track.cs

@@ -133,6 +133,7 @@ namespace Perspex.Controls.Primitives
                 {
                     var width = Math.Max(finalSize.Width * thumbFraction, thumb.MinWidth);
                     var x = (finalSize.Width - width) * valueFraction;
+                    System.Diagnostics.Debug.WriteLine("" + this.Value + " " + x);
                     thumb.Arrange(new Rect(x, 0, width, finalSize.Height));
                 }
                 else

Perspex.Layout/LayoutManager.cs

@@ -198,11 +198,12 @@ namespace Perspex.Layout
                 {
                     this.Root.Arrange(new Rect(this.Root.ClientSize));
                 }
-                else
+
+                foreach (var item in arrange)
                 {
-                    foreach (var item in arrange)
+                    if (!item.Control.IsArrangeValid)
                     {
-                        if (!item.Control.IsArrangeValid)
+                        if (item.Control != this.Root)
                         {
                             var control = item.Control;