Please run the attached sample project and load the XML file (test3.xml) located in the folder. After 4-5 times loading the file, the  application freezes.

In this particular case, the connections are added runtime which triggers the exception when the TipOverTree is routing is used.

To reproduce: 
- Add DiagramRibbonBar to a user control.
- Try setting the AssociatedControl from the smart tag.
- An error message will be shown.

Workaround:
Set it in code:
radDiagramRibbonBar1.AssociatedDiagram = radDiagram1;

How to reproduce: check the attached video - unexpected-behavior.gif

To reproduce: 
Bind using a binding source:
DataSet ds = new DataSet();
ds.Tables.Add(shapesTable);
ds.Tables.Add(connectionsTable);

BindingSource bindingSource1 = new BindingSource { DataSource = ds };

radDiagram1.DiagramElement.DataLayer.DataSource = bindingSource1;


Workaround: 
Bind directly:
DataSet ds = new DataSet();
ds.Tables.Add(shapesTable);
ds.Tables.Add(connectionsTable);

radDiagram1.DiagramElement.DataLayer.DataSource = ds;

To reproduce
- Click between the thumb and the button.

Workaround:
public class MyDiagramInputBehavior : DiagramInputBehavior
{
    public MyDiagramInputBehavior(RadDiagramElement element) : base(element)
    {


    }
    protected override bool IsScrollBar(RadElement element)
    {
        if (element != null && element is RadScrollBarElement)
        {
            return true;
        }
        return base.IsScrollBar(element);
    }
}

To reproduce:

public Form1()
{
    InitializeComponent();

    this.radDiagram1.SelectionMode = Telerik.Windows.Diagrams.Core.SelectionMode.None;
    PopulateWithData();
}

private void PopulateWithData()
{
    DataTable tasksTable = new DataTable("Tasks");   
    tasksTable.Columns.Add("Id");
    tasksTable.Columns.Add("Text");
    tasksTable.Columns.Add("Type");
    tasksTable.Columns.Add("X");
    tasksTable.Columns.Add("Y");
    tasksTable.Columns.Add("Width");
    tasksTable.Columns.Add("Height");
    tasksTable.Rows.Add("Task1", "Task 1", "circle", 100, 300, 50, 50);
    tasksTable.Rows.Add("Task2", "Task 2", "rectangle", 200, 100, 100, 100);
    tasksTable.Rows.Add("Task3", "Task 3", "circle", 300, 300, 50, 50);
    tasksTable.Rows.Add("Task4", "Task 4", "rectangle", 400, 100, 100, 100);
    tasksTable.Rows.Add("Task5", "Task 5", "circle", 500, 300, 50, 50);

    DataTable relationsTable = new DataTable("Relations");
    relationsTable.Columns.Add("SourceTaskId");
    relationsTable.Columns.Add("SourceConnector");
    relationsTable.Columns.Add("TargetTaskId");
    relationsTable.Columns.Add("TargetConnector");
    relationsTable.Columns.Add("StartCapField");
    relationsTable.Columns.Add("EndCapField");
    relationsTable.Rows.Add("Task2", "Left", "Task1", "Auto", "Arrow5Filled", "Arrow1");
    relationsTable.Rows.Add("Task2", "Auto", "Task3", "Auto", "Arrow4Filled", "Arrow1Filled");
    relationsTable.Rows.Add("Task4", "Auto", "Task5", "Auto", "Arrow2Filled", "Arrow2");

    DataSet ds = new DataSet();
    ds.Tables.Add(tasksTable);
    ds.Tables.Add(relationsTable);

    this.radDiagram1.DataSource = ds;

    this.radDiagram1.ConnectionDataMember = "Relations";
    this.radDiagram1.ShapeDataMember = "Tasks";
    this.radDiagram1.ShapeIdMember = "Id";  
    this.radDiagram1.ShapeTextMember = "Text";
    this.radDiagram1.ShapeTypeMember = "Type";
    this.radDiagram1.ShapeXMember = "X";
    this.radDiagram1.ShapeYMember = "Y";
    this.radDiagram1.ShapeWidthMember = "Width";
    this.radDiagram1.ShapeHeightMember = "Height";

    this.radDiagram1.ConnectionSourceShapeIdMember = "SourceTaskId";
    this.radDiagram1.ConnectionTargetShapeIdMember = "TargetTaskId";
    this.radDiagram1.ConnectionSourceCapTypeMember = "StartCapField";
    this.radDiagram1.ConnectionTargetCapTypeMember = "EndCapField";

    this.radDiagram1.ConnectionSourceConnectorMember = "SourceConnector";
    this.radDiagram1.ConnectionTargetConnectorMember = "TargetConnector";
}

Workaround: after rebinding, clear the selection and set the SelectionMode to None:

PopulateWithData();
this.radDiagram1.SelectedItem = null;
this.radDiagram1.SelectionMode = Telerik.Windows.Diagrams.Core.SelectionMode.None;

To reproduce:
- Add shape to the diagram.
- Select the shape. 
- Press and hold Ctrl, then press one of the arrow keys.
- The shape is not moved.

Workaround:
private void RadDiagram1_KeyDown(object sender, KeyEventArgs e)
{
   // Ctrl should be pressed as well.
    if (e.KeyCode == Keys.Left)
    {
        var shape = radDiagram1.SelectedItem as RadDiagramShape;
        if (shape != null)
        {
            shape.Position = new Telerik.Windows.Diagrams.Core.Point(shape.Position.X - 10, shape.Position.Y);
        }
    }
}

To reproduce:
radDiagram1.SelectedItem = radDiagram1.Shapes[2];

Workaround:
radDiagram1.Shapes[2].IsSelected = true;

Note: this behavior may be applied to all other relevant manipulation properties

To reproduce:

            this.radDiagram1.IsDraggingEnabled = true;
            RadDiagramShape shape1 = new RadDiagramShape();
            shape1.Text = "Shape1";
            shape1.BackColor = Color.Red;
            shape1.IsDraggingEnabled = false;
            shape1.ElementShape = new RoundRectShape(5);
            this.radDiagram1.Items.Add(shape1);

As a result you will be able to drag the shape which is not correct.

Workaround: set the RadDiagramShape.IsDraggingEnabled  after the shape is added to the diagram:

this.radDiagram1.IsDraggingEnabled = true;
RadDiagramShape shape1 = new RadDiagramShape();
shape1.Text = "Shape1";
shape1.BackColor = Color.Red;         
shape1.ElementShape = new RoundRectShape(5);
this.radDiagram1.Items.Add(shape1);
shape1.IsDraggingEnabled = false;

Please refer to the attached gif file.

Workaround:  cancel the PreviewPan event and adjust manually the  Telerik.WinControls.UI.Diagrams.Panel.PositionOffset. Here is demonstrated a sample approach:
int widthOffset = -1000;
int heightOffset = -1000;

private void radDiagram_PreviewPan(object sender, Telerik.WinControls.UI.Diagrams.PositionChangedRoutedEventArgs e)
{
    Telerik.WinControls.UI.Diagrams.Panel panel = this.radDiagram.DiagramElement.Children.First() as Telerik.WinControls.UI.Diagrams.Panel;
    Telerik.WinControls.UI.Diagrams.Panel hitTestablePanel = panel.Children.First() as Telerik.WinControls.UI.Diagrams.Panel;

    e.Cancel = true;
    if (panel != null)
    {
        hitTestablePanel.PositionOffset = new SizeF(widthOffset,heightOffset);
        widthOffset += 50;
    }
}

To reproduce: 
1. Add RadDiagram with 10 shapes and connection between them 
2. Set the Layout to be Tree
3. The vertical scrollbar is not layout to the end of diagram, there is a gap. 

http://docs.telerik.com/devtools/wpf/controls/raddiagram/extensions/thumbnail