KeyNotFoundException with MDS layout

Hi Lev,
I tried to modify WpfAplicationSample to show MDS layout, and it throws KeyNotFoundException.
Here are my modifications:

diff --git a/GraphLayout/Samples/WpfApplicationSample/WpfApplicationSample.cs b/GraphLayout/Samples/WpfApplicationSample/WpfApplicationSample.cs
index 5a6e6dd..f16ec58 100644
--- a/GraphLayout/Samples/WpfApplicationSample/WpfApplicationSample.cs
+++ b/GraphLayout/Samples/WpfApplicationSample/WpfApplicationSample.cs
@@ -291,6 +291,7 @@ namespace WpfApplicationSample
 //                //graph.LayoutAlgorithmSettings.EdgeRoutingSettings.EdgeRoutingMode = EdgeRoutingMode.SplineBundling;
 //                //layout the graph and draw it
                 Graph graph = new Graph();
+                graph.LayoutAlgorithmSettings=new Microsoft.Msagl.Layout.MDS.MdsLayoutSettings();
                 graph.AddEdge("47", "58");
                 graph.AddEdge("70", "71");

@@ -315,11 +316,11 @@ namespace WpfApplicationSample
                 graph.Attr.LayerDirection = LayerDirection.LR;
                 //graph.LayoutAlgorithmSettings.EdgeRoutingSettings.EdgeRoutingMode = EdgeRoutingMode.Rectilinear;

-                var global = (SugiyamaLayoutSettings) graph.LayoutAlgorithmSettings;
-                var local  = (SugiyamaLayoutSettings) global.Clone();
-                local.Transformation = PlaneTransformation.Rotation(-Math.PI / 2);
+                var global = (Microsoft.Msagl.Layout.MDS.MdsLayoutSettings) graph.LayoutAlgorithmSettings;
+                var local  = (Microsoft.Msagl.Layout.MDS.MdsLayoutSettings) global.Clone();
+                //local.Transformation = PlaneTransformation.Rotation(-Math.PI / 2);
                 subgraph2.LayoutSettings = local;   // for Collapsing\Expanding
-                global.ClusterSettings.Add(subgraph2, local);
+                //global.ClusterSettings.Add(subgraph2, local);

                 graphViewer.Graph = graph;
             }

The line, which throws exception is:

                intEdges.Add(new SimpleIntEdge {Source = nodeIndex[e.Source], Target = nodeIndex[e.Target]});

Checking with debugger, I can see that subgraph2 is missing from nodeIndex dictionary.

I have no idea why it happens specifically with MDS, but doesn't happen with Sugiyama.
Am I doing something wrong, or is there a bug in MDS layout algorithm?
Here's the screenshot of the exception being thrown:

Reproduce the exception in GraphLayout/Samples/WpfApplicationSample/WpfApplicationSample.cs using MdsLayoutSettings and the shown subgraph configuration. Start at the SimpleIntEdge construction where nodeIndex[e.Source] and nodeIndex[e.Target] are accessed, then trace how the MDS layout builds nodeIndex and handles subgraph2. Done means the sample no longer throws KeyNotFoundException for this layout.