To reproduce: 
1.Add a RadTreeView and four RadButton controls.
2.Use the following code snippet:

private Random random = new Random();

public Form1()
{
    InitializeComponent();

    radTreeView1.AutoSize = true;
    radTreeView1.TreeViewElement.HorizontalScrollState = ScrollState.AlwaysHide ;
    radTreeView1.TreeViewElement.DrawBorder = false;
}

private string NextText()
{
    char[] letters = new char[random.Next(4, 11)];
    for (int i = 0; i < letters.Length; ++i)
    {
        letters[i] = (char)random.Next('a', 'z' + 1);
    }
    letters[0] = char.ToUpper(letters[0]);
    return new string(letters);
}

private RadTreeNodeCollection GetRandomNodeCollection()
{
    if (radTreeView1.Nodes.Count == 0)
    {
        return radTreeView1.Nodes;
    }

    int depth = random.Next(MaxDepth(radTreeView1.Nodes));

    var source = radTreeView1.Nodes;
    while ((depth--) >= 0 && source.Count > 0)
    {
        source = source[random.Next(source.Count)].Nodes;
    }

    return source;
}

private static int MaxDepth(RadTreeNodeCollection nodes, int currentDepth = 0)
{
    if (nodes.Count == 0)
    {
        return currentDepth;
    }

    int max = -1;

    foreach (var n in nodes)
    {
        max = Math.Max(MaxDepth(n.Nodes, currentDepth + 1), max);
    }

    return max;
}

private void UpdateTree(bool clearNodes)
{
    radTreeView1.BeginUpdate();
    if (clearNodes)
    {
        radTreeView1.Nodes.Clear();   
    }
    else
    {
        bool makeRoot = false;

        int count = random.Next(10, 50);
        for (; count > 0; --count)
        {
            makeRoot = random.NextDouble() < 0.23456789;
            var nodes = makeRoot
                        ? radTreeView1.Nodes
                        : GetRandomNodeCollection();
            
            nodes.Add(NextText());
        }
    }
    radTreeView1.EndUpdate();
    radTreeView1.ExpandAll();
}

private void radButton1_Click(object sender, EventArgs e)
{
    UpdateTree(false);
}

private void radButton2_Click(object sender, EventArgs e)
{
    UpdateTree(true);
}

private void radButton3_Click(object sender, EventArgs e)
{
    radTreeView1.ExpandAll();
}

private void radButton4_Click(object sender, EventArgs e)
{
    radTreeView1.CollapseAll();
}


Workaround: instead of clearing nodes, remove one by one:

//radTreeView1.Nodes.Clear();
while (radTreeView1.Nodes.Count > 0)
{
    radTreeView1.Nodes.Last().Remove();
}

To reproduce use the following function to reset the data source of the treeview
public void LoadObjects()
{
    radBreadCrumb1.DefaultTreeView = null;

    tvObjects.DataSource = null;
    
    tvObjects.DataSource = GetTable();
    tvObjects.DisplayMember = "Name";
    tvObjects.ValueMember = "Name";
    
    radBreadCrumb1.DefaultTreeView = tvObjects;
}

Workaround:
public void LoadObjects()
{
    radBreadCrumb1.DefaultTreeView = null;

    MethodInfo mi = typeof(RadBreadCrumb).GetMethod("value_Selected", BindingFlags.Instance | BindingFlags.NonPublic);
    Delegate delegateToRemove = Delegate.CreateDelegate(typeof(RadTreeView.RadTreeViewEventHandler), this.radBreadCrumb1, mi);

    this.tvObjects.TreeViewElement.SelectedNodeChanged -= (RadTreeView.RadTreeViewEventHandler)delegateToRemove;

    mi = typeof(RadBreadCrumb).GetMethod("value_NodeExpand", BindingFlags.Instance | BindingFlags.NonPublic);
    delegateToRemove = Delegate.CreateDelegate(typeof(RadTreeView.TreeViewEventHandler), this.radBreadCrumb1, mi);

    this.tvObjects.TreeViewElement.NodeExpandedChanged -= (RadTreeView.TreeViewEventHandler)delegateToRemove;
 
    tvObjects.DataSource = null;
    
    tvObjects.DataSource = GetTable();
    tvObjects.DisplayMember = "Name";
    tvObjects.ValueMember = "Name";
    
    radBreadCrumb1.DefaultTreeView = tvObjects;
}

To reproduce: add a hierarchical RadTreeView with several levels. Use the  RadTreeNode.Expanded property in order to expand a child node from the bottom levels. Ensure that all parent nodes up to the top are expanded as well. When you run the application, the vertical scroll bar is not displayed.

Sub New()
    InitializeComponent()
    Me.Size = New Size(234, 188)
    Dim dt As New DataTable
    dt.Columns.Add("Id", GetType(String))
    dt.Columns.Add("ParentId", GetType(String))
    dt.Columns.Add("Name", GetType(String))

    Dim uniqueId As String = Guid.NewGuid().ToString()
    dt.Rows.Add(uniqueId, Nothing, "Node.1")
    For index = 2 To 5
        Dim subUniqueId As String = Guid.NewGuid().ToString()
        dt.Rows.Add(subUniqueId, uniqueId, "SubNode.1." & index)
        If index Mod 2 = 0 Then
            For index2 = 6 * index To 6 * index + 5
                Dim subSubUniqueId As String = Guid.NewGuid().ToString()
                dt.Rows.Add(subSubUniqueId, subUniqueId, "SubSubNode.1." & index & "." & index2)
                For index3 = 12 * index To 12 * index + 3
                    Dim subSubSubUniqueId As String = Guid.NewGuid().ToString()
                    dt.Rows.Add(subSubSubUniqueId, subSubUniqueId, "SubSubSubNode.1." & index & "." & index2 & "." & index3)
                Next
            Next
        End If
    Next

    Me.RadTreeView1.DataSource = dt
    Me.RadTreeView1.DisplayMember = "Name"
    Me.RadTreeView1.ValueMember = "Id"
    Me.RadTreeView1.RelationBindings.Add(New RelationBinding(dt, "Name", "ParentId", "Id", "Id"))

End Sub

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim nodeTextToExpand = "SubSubNode.1.4.27"
    Dim nodeToExpand = Me.RadTreeView1.GetNodeByName(nodeTextToExpand)
    If nodeToExpand IsNot Nothing Then
        Expand(nodeToExpand)
    End If
End Sub

Private Sub Expand(nodeToExpand As RadTreeNode)
    nodeToExpand.Expanded = True
    If nodeToExpand.Parent IsNot Nothing Then
        Expand(nodeToExpand.Parent)
    End If
End Sub

Workaround: start expanding the nodes from the top most level to the bottom most level: 
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim nodeTextToExpand = "SubSubNode.1.4.27"
    Dim nodeToExpand = Me.RadTreeView1.GetNodeByName(nodeTextToExpand)
    If nodeToExpand IsNot Nothing Then
        Expand(nodeToExpand)
    End If

    While (nodes.Count > 0)
        nodes.Pop().Expanded = True
    End While
End Sub

Dim nodes As New Stack(Of RadTreeNode)
Private Sub Expand(nodeToExpand As RadTreeNode)       
    nodes.Push(nodeToExpand)
    If nodeToExpand.Parent IsNot Nothing Then
        Expand(nodeToExpand.Parent)
    End If
End Sub

To reproduce: use the following code

public class Item
{
    public int Id { get; set; }

    public string Title { get; set; }

    public string Tag { get; set; }

    public Item(int id, string title, string tag)
    {
        this.Id = id;
        this.Title = title;
        this.Tag = tag;
    }
}

public Form1()
{
    InitializeComponent();

    List<Item> items = new List<Item>();
    items.Add(new Item(1,"a1","x1"));
    items.Add(new Item(2,"a2","x2"));
    items.Add(new Item(3,"a3","x3"));
    items.Add(new Item(4,"b1","y1"));
    items.Add(new Item(5,"b2","y2"));
    items.Add(new Item(6,"b3","y3"));
    this.radTreeView1.DataSource = items;
    this.radTreeView1.DisplayMember = "Title";
    this.radTreeView1.ValueMember = "Id";
   
    radTreeView1.FilterDescriptors.Add(new FilterDescriptor("Tag", FilterOperator.Contains, "y"));
}

Workaround: use custom filtering:
public Form1()
{
    InitializeComponent();

    List<Item> items = new List<Item>();
    items.Add(new Item(1,"a1","x1"));
    items.Add(new Item(2,"a2","x2"));
    items.Add(new Item(3,"a3","x3"));
    items.Add(new Item(4,"b1","y1"));
    items.Add(new Item(5,"b2","y2"));
    items.Add(new Item(6,"b3","y3"));
    this.radTreeView1.DataSource = items;
    this.radTreeView1.DisplayMember = "Title";
    this.radTreeView1.ValueMember = "Id";
   
    radTreeView1.FilterDescriptors.Add(new FilterDescriptor("Tag", FilterOperator.Contains, "y")); 
    radTreeView1.TreeViewElement.FilterPredicate = FilterNode;
}

public class Item
{
    public int Id { get; set; }

    public string Title { get; set; }

    public string Tag { get; set; }

    public Item(int id, string title, string tag)
    {
        this.Id = id;
        this.Title = title;
        this.Tag = tag;
    }
}

private bool FilterNode(RadTreeNode node)
{
    Item item = node.DataBoundItem as Item;
  
    if (item != null && radTreeView1.FilterDescriptors.Count > 0)
    { 
        FilterDescriptor fd = radTreeView1.FilterDescriptors[0];
        var propertyValue = item.GetType().GetProperty(fd.PropertyName,
            BindingFlags.Public | BindingFlags.Instance).GetValue(item, null);
        if (propertyValue.ToString().Contains(fd.Value.ToString()))
        {
            return true;
        }
        return false;
    }

    return false;
}

To reproduce : add a RadTreeView with several nodes and use the following code snippet:

this.radTreeView1.AllowDragDrop = true;
this.TopMost = true;

Note that dragging a node will no longer display the "DropHint" line.

Workaround:

class CustomDragDropService : TreeViewDragDropService
{
    public CustomDragDropService(RadTreeViewElement owner) : base(owner)
    {
    }

    protected override void UpdateHintPosition(Point mousePosition)
    {
        FieldInfo fi = typeof(TreeViewDragDropService).GetField("dropHintWindow",
            BindingFlags.NonPublic | BindingFlags.Instance);
       
        RadLayeredWindow window = fi.GetValue(this) as RadLayeredWindow;
        window.TopMost = true;
        base.UpdateHintPosition(mousePosition);
    }
}

class CustomTreeViewElement : RadTreeViewElement
{
    //Enable themeing for the element
    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(RadTreeViewElement);
        }
    }

    //Replace the default drag drop service with the custom one
    protected override TreeViewDragDropService CreateDragDropService()
    {
        return new CustomDragDropService(this);
    }
}

class CustomTreeView : RadTreeView
{
    //Replace the default element with the custom one
    protected override RadTreeViewElement CreateTreeViewElement()
    {
        return new CustomTreeViewElement();
    }

    //Enable theming for the control
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadTreeView).FullName;
        }
    }
}

To reproduce:
- Add RadTreeView to a blank form.
- Set its AllowDragDrop and AllowDefaultContextMenu properties to true.
- Clear the menu items in the  ContextMenuOpening event.
- You will notice that the Copy, Cut and Paste items are not removed.

Workaround:
 void radTreeView1_ContextMenuOpening(object sender, Telerik.WinControls.UI.TreeViewContextMenuOpeningEventArgs e)
{
   
    e.Menu.DropDownOpened -= Menu_DropDownOpened; 
    e.Menu.DropDownOpened += Menu_DropDownOpened; 
}

void Menu_DropDownOpened(object sender, EventArgs e)
{
    TreeViewDefaultContextMenu Menu = sender as TreeViewDefaultContextMenu;

    for (int i = Menu.Items.Count - 1; i >= 0; i--)
    {
        if (Menu.Items[i].Name == "Copy" || Menu.Items[i].Name == "Cut" || Menu.Items[i].Name == "Paste")
        {
            Menu.Items.Remove(Menu.Items[i]);
        }
    }
}

Add a RadTreeView with several hierarchy levels. Initially all nodes are collapsed. When you collapse each child node deeper in the hierarchy, use the following code snippet:

public Form1()
{
    InitializeComponent();

    radTreeView1.CollapseAll();
    radTreeView1.TreeViewElement.AutoScrollOnClick = false;
}

private void radTreeView1_NodeExpandedChanged(object sender, RadTreeViewEventArgs e)
        {
            if (e.Node.Expanded)
            {
                e.Node.LastNode.EnsureVisible();
                radTreeView1.BringIntoView(e.Node.LastNode);
            }
        }
		
The last child node is visible, regarding the height, however, the entire node is not visible, regarding the width.

Workaround: use RadTreeView.MouseUp event instead.

private void radTreeView1_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        TreeNodeExpanderItem expander = radTreeView1.ElementTree.GetElementAtPoint(e.Location) as TreeNodeExpanderItem;
        if (expander != null && expander.Expanded && expander.NodeElement.Data != null)
        {
            radTreeView1.BringIntoView(expander.NodeElement.Data.LastNode);
        }
    }
}

To reproduce:
- Add treeview to a form and set its AutoScrollOnClick property to false.
- click a node that is not entirely visible with the right mouse button.
- You will notice that the view is auto scrolled.

To reproduce
- Add RadTreeView with some nodes to a blank form.
- Set the MultiSelect property to true.
- Select\Deselect a node with code.
 
Resolution: 
The SelectedNodeChanged event should not be fired when selected/deselected the node programmatically. We added a new event SelectedNodesChanged which is fired when the SelectedNodes collection changes.

To reproduce: 


protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);


    radTreeView1 = new RadTreeView();
    radTreeView1.Parent = this;


    for (int i = 0; i < 5; i++)
    {
        RadTreeNode n1 = new RadTreeNode("Node" + i);
        this.radTreeView1.Nodes.Add(n1);
        if (i % 2 == 0)
        {
            for (int j = 0; j < 2; j++)
            {
                RadTreeNode n2 = new RadTreeNode("Node" + i + "." + j);
                n1.Nodes.Add(n2);


                if (j % 2 == 0)
                {
                    for (int k = 0; k < 2; k++)
                    {
                        RadTreeNode n3 = new RadTreeNode("Node" + i + "." + j + "." + k);
                        n2.Nodes.Add(n3);
                    }
                }
            }
        }
    }
    radTreeView1.ShowRootLines = false;
    radTreeView1.ShowLines = false;
}


Workaround:

void radTreeView1_NodeFormatting(object sender, TreeNodeFormattingEventArgs e)
{
    if (radTreeView1.ShowLines == false)
    {
        if (e.NodeElement.LinesContainerElement.Children.Count > 0)
        {
            TreeNodeLineElement lineElement = (TreeNodeLineElement)e.NodeElement.LinesContainerElement.Children[0];
            lineElement.Visibility = ElementVisibility.Collapsed;
        }
    }
}

To reproduce:

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);


    radTreeView1 = new RadTreeView();
    radTreeView1.Parent = this;


    for (int i = 0; i < 5; i++)
    {
        RadTreeNode n1 = new RadTreeNode("Node" + i);
        this.radTreeView1.Nodes.Add(n1);
        if (i % 2 == 0)
        {
            for (int j = 0; j < 2; j++)
            {
                RadTreeNode n2 = new RadTreeNode("Node" + i + "." + j);
                n1.Nodes.Add(n2);


                if (j % 2 == 0)
                {
                    for (int k = 0; k < 2; k++)
                    {
                        RadTreeNode n3 = new RadTreeNode("Node" + i + "." + j + "." + k);
                        n2.Nodes.Add(n3);
                    }
                }
            }
        }
    }
    radTreeView1.ShowRootLines = true;
    radTreeView1.ShowExpandCollapse = false;
    radTreeView1.ShowLines = true;
}


WORKAROUND: 
        void radTreeView1_NodeFormatting(object sender, TreeNodeFormattingEventArgs e)
        {
            if (radTreeView1.ShowExpandCollapse == false && radTreeView1.ShowRootLines == true)
            {
                if (e.Node.Parent == null && e.Node.Nodes.Count >0)
                {
                    TreeNodeLineElement lineElement = (TreeNodeLineElement)e.NodeElement.LinesContainerElement.Children[0];
                    lineElement.Visibility = ElementVisibility.Visible;
                    if (e.Node.Index==0)
                    {
                        lineElement.Type = TreeNodeLineElement.LinkType.RightTopAngleShape;
                    }
                    else if (e.Node.Index == radTreeView1.Nodes.Count -1)
                    {
                        lineElement.Type = TreeNodeLineElement.LinkType.RightBottomAngleShape;
                    }
                }
            }
        }

Start dragging a node and scroll using the mouse wheel. While scrolling, drop the node. 

To reproduce:
-add RadTreeView and RadButton:
-use the following code:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        List<Distributor> distributors = new List<Distributor>()
        {
            new Distributor(432,"Distributor 1"),
            new Distributor(454,"Distributor 2"),
            new Distributor(438,"Distributor 3"),
            new Distributor(455,"Distributor 4")
        };

        List<Distributor> distributors2 = new List<Distributor>()
        {
            new Distributor(486,"Distributor 5"),
            new Distributor(487,"Distributor 6"),
            new Distributor(498,"Distributor 7"),
            new Distributor(475,"Distributor 8")
        };

        List<Product> products = new List<Product>();
        products.Add(new Product(567, "Bicycle", 5, distributors));
        products.Add(new Product(456, "Car", 5000,distributors2));
        products.Add(new Product(789, "Bike", 1500,null));

        BindingList<Category> categories = new BindingList<Category>();
        categories.Add(new Category("Bikes", products));
        categories.Add(new Category("Accessories", null));
        categories.Add(new Category("Clothing", null));

        radTreeView1.DataSource = categories;
        if ((radTreeView1.DataSource as BindingList<Category>).Count > 0)
        {
            radTreeView1.DisplayMember = "Name\\Description\\Name";
            radTreeView1.ChildMember = "Categories\\Products\\Distributors";   
        }
        
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        BindingList<Category> categories = radTreeView1.DataSource as BindingList<Category>;
        categories.Clear();
    }
}

public class Distributor
{
    private int _id;
    private string _name;

    public Distributor(int id, string name)
        {
            this._id = id;
            this._name = name;
        }

    public int Id
        {
            get
            {
                return this._id;
            }
            set
            {
                this._id = value;
            }
        }

    public string Name
        {
            get
            {
                return this._name;
            }
            set
            {
                this._name = value;
            }
        }
}

public class Product
{
    private int _id;
    private string _description;
    private float _price;
    private List<Distributor> _distributors;

    public List<Distributor> Distributors
        {
            get
            {
                return this._distributors;
            }
            set
            {
                this._distributors = value;
            }
        }

    public int ID
        {
            get
            {
                return _id;
            }
            set
            {
                _id = value;
            }
        }

    public string Description
        {
            get
            {
                return _description;
            }
            set
            {
                _description = value;
            }
        }

    public float Price
        {
            get
            {
                return _price;
            }
            set
            {
                _price = value;
            }
        }

    public Product(int id, string description, float price, List<Distributor> distributors)
    {
        _id = id;
        _description = description;
        _price = price;
        _distributors = distributors;
    }
}

public class Category
{
    public Category(string name, List<Product> products)
    {
        _name = name;
        _products = products;
    }

    private List<Product> _products;
    private string _name;

    public string Name
        {
            get
            {
                return _name;
            }
            set
            {
                _name = value;
            }
        }

    public List<Product> Products
        {
            get
            {
                return _products;
            }
            set
            {
                _products = value;
            }
        }
}

When you click the button, ArgumentOutOfRangeException is thrown.

Workaround: instead of clearing the BindingList, remove each list item one by one:
while (categories.Count>0)
{
    categories.RemoveAt(0);
}

Workaround:
Instead of {RadTreeNode}.Nodes.Clear(), use 

 while ({RadTreeNode}.Nodes.Count>0)
          {
              {RadTreeNode}.Nodes.RemoveAt(0);
          }

To reproduce:
- Add a RadTreeView which have parent and child nodes to a form.
- Expand nodes until the both scrollbars are simultaneously shown.
- You will notice that you cannot scroll to the last item.

Workaround:
- Subscribe to the following ScrollerUpdated event handler:

void Scroller_ScrollerUpdated(object sender, EventArgs e)
{
radTreeView1.TreeViewElement.InvalidateMeasure();

}

- You can subscribe to this event with the following line of code:
radTreeView1.TreeViewElement.Scroller.ScrollerUpdated += Scroller_ScrollerUpdated;

To reproduce: 
Add a RadTreeView to a form and use the following code:
private List<EntityA> entities = new List<EntityA>(); public Form1() { InitializeComponent(); radTreeView1.TriStateMode = true; entities = new List<EntityA>(); for (int i = 0; i < 10; i++) { var newEntityI = new EntityA(i.ToString()); for (int j = 0; j < 100; j++) { var newEntityJ = new EntityB(j.ToString()); for (int k = 0; k < 1000; k++) { var newEntityK = new EntityC(k.ToString()); newEntityJ.Entities.Add(newEntityK); } newEntityI.Entities.Add(newEntityJ); } entities.Add(newEntityI); } } private void checkBox1_CheckedChanged(object sender, EventArgs e) { foreach (var node in radTreeView1.Nodes) { node.Checked = checkBox1.Checked; } } private void radTreeView1_NodesNeeded(object sender, NodesNeededEventArgs e) { if (e.Parent == null) { foreach (var entity in entities) { e.Nodes.Add(new RadTreeNode(entity.Name, false) { CheckState = ToggleState.Off, Tag = entity }); } } else if (e.Parent.Tag is EntityA) { var currentEntity = e.Parent.Tag as EntityA; foreach (var entity in currentEntity.Entities) { e.Nodes.Add(new RadTreeNode(entity.Name, false) { CheckState = e.Parent.CheckState, Tag = entity }); } } else if (e.Parent.Tag is EntityB) { var currentEntity = e.Parent.Tag as EntityB; foreach (var entity in currentEntity.Entities) { e.Nodes.Add(new RadTreeNode(entity.Name, false) { CheckState = e.Parent.CheckState, Tag = entity }); } } else if (e.Parent.Tag is EntityC) { } } 
Put a breakpoint in the last If statement, you will notice that the breakpoint is being hit, while it is not if the TrieStateMode is set to false 

Workaround: 
Use the following custom RadTreeNode: 
public class MyTreeNode : RadTreeNode { private FieldInfo triStateField; public MyTreeNode() : base() { } public MyTreeNode(string text) : base(text) { } public MyTreeNode(string text, RadTreeNode[] children) : base(text, children) { } public MyTreeNode(string text, bool expanded) : base(text, expanded) { } public MyTreeNode(string text, Image image) : base(text, image) { } public MyTreeNode(string text, Image image, bool expanded) : base(text, image, expanded) { } public override ToggleState CheckState { get { return base.CheckState; } set { bool set = false; if (this.TreeViewElement != null && this.TreeViewElement.TriStateMode) { if (this.triStateField == null) { this.triStateField = typeof(RadTreeViewElement).GetField("triStateMode", BindingFlags.Instance | BindingFlags.NonPublic); } triStateField.SetValue(this.TreeViewElement, false); set = true; } base.CheckState = value; if (set) { this.triStateField.SetValue(this.TreeViewElement, true); } } } }

To reproduce: Add a RadTreeView with hierarchical data. Select a node with hierarchy level > 0. Call the Clear method of the Nodes collection. Refill the tree, drag and drop a node, you will see that two nodes will be dropped since the previous node's Selected property is set to true. 

Workaround: private void DetachAllNodes(RadTreeNode parent) { this.CleanNode(parent); foreach (RadTreeNode node in parent.Nodes) { this.DetachAllNodes(node); } } private void CleanNode(RadTreeNode node) { node.Current = false; node.Selected = false; } foreach (RadTreeNode node in tree.Nodes) { this.DetachAllNodes(node); } tree.Nodes.Clear();

Workaround:
this.radTreeView1.SelectedNode = null;

To reproduce: this issue is reproducible under Windows8 OS only
-add RadTreeView from the Toolbox to the Form and add several tree nodes at design time;
-add RadContextMenu from the Toolbox and add several items at design time;
Use the following code:
public Form1()
{
    InitializeComponent();

    this.radTreeView1.RadContextMenu = this.radContextMenu1;
}
-run the application;
-select a tree node;
-right mouse click over the node to show the context menu; As a result the main form looses focus and you are unable to click anywhere outside the RadTreeView.
This issue is inconstant and it is not appearing every time.

Workaround: use ContextMenu property instead:
public Form1()
{
    InitializeComponent();

    ContextMenu menu = new ContextMenu();

    foreach (var item in radContextMenu1.Items)
    {
        menu.MenuItems.Add(new MenuItem(item.Text));
    }

    this.radTreeView1.ContextMenu = menu;
    // this.radTreeView1.RadContextMenu = this.radContextMenu1;
}

To reproduce:
Add a RadTreeView with some nodes and you will notice that the font is different than other controls.

Workaround:
void tree_NodeFormatting(object sender, TreeNodeFormattingEventArgs e)
{
    e.NodeElement.ContentElement.TextRenderingHint = System.Drawing.Text.TextRenderingHint.SystemDefault;
}