How to reproduce:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        this.radGridView1.DataSource = this.GetData();
        this.Load += Form1_Load;
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        this.radGridView1.SynchronizeCurrentRowInSplitMode = true;
        this.radGridView1.SplitMode = Telerik.WinControls.UI.RadGridViewSplitMode.Vertical;
    }

    private DataTable GetData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Name", typeof(string));
        dt.Columns.Add("Age", typeof(int));
        dt.Columns.Add("Date", typeof(DateTime));
        dt.Columns.Add("Bool", typeof(bool));
        for (int i = 0; i < 100; i++)
        {
            dt.Rows.Add("Name " + i, i, DateTime.Now.AddMinutes(i), i % 2 == 0 ? true : false);
        }

        return dt;
    }
}



Workaround: 

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        this.radGridView1.DataSource = this.GetData();
        this.radGridView1.ViewDefinition = new SplitViewDefintion();
        this.Load += Form1_Load;
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        this.radGridView1.SynchronizeCurrentRowInSplitMode = true;
        this.radGridView1.SplitMode = Telerik.WinControls.UI.RadGridViewSplitMode.Vertical;
    }

    private DataTable GetData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Name", typeof(string));
        dt.Columns.Add("Age", typeof(int));
        dt.Columns.Add("Date", typeof(DateTime));
        dt.Columns.Add("Bool", typeof(bool));
        for (int i = 0; i < 100; i++)
        {
            dt.Rows.Add("Name " + i, i, DateTime.Now.AddMinutes(i), i % 2 == 0 ? true : false);
        }

        return dt;
    }
}

public class SplitViewDefintion : TableViewDefinition
{
    public override IRowView CreateViewUIElement(GridViewInfo viewInfo)
    {
        return new MyGridTableElement();
    }
}

public class MyGridTableElement : GridTableElement
{
    protected override RadScrollBarElement CreateScrollBarElement()
    {
        return new MyRadScrollbarElement();
    }
}

public class MyRadScrollbarElement : RadScrollBarElement
{
    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(RadScrollBarElement);
        }
    }

    protected override void OnMouseDown(MouseEventArgs e)
    {
        if (Cursor.Current == Cursors.SizeWE || Cursor.Current == Cursors.SizeNS)
        {
            return;
        }

        base.OnMouseDown(e);
    }
}

To reproduce: 

1. Bind RadGridView to a collection of business objects where one of the properties is Nullable<DateTime>.
2. Leave one of the items with an empty date (null value).
3. Copy the entire row and try to paste in one of the grid rows. The FormatException is thrown.

Sub New()
    InitializeComponent()

    Dim items As New List(Of Item)

    items.Add(New Item(1, DateTime.Now.AddDays(2), "Item1"))
    items.Add(New Item(2, Nothing, "Item2"))
    items.Add(New Item(3, DateTime.Now.AddDays(4), "Item3"))
    items.Add(New Item(4, DateTime.Now.AddDays(5), "Item4"))

    Me.RadGridView1.DataSource = items
    Me.RadGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill 
End Sub

Public Class Item
    Private _id As Integer
    Private _createdOn As Nullable(Of DateTime)
    Private _title As String

    Public Sub New(id As Integer, createdOn As Nullable(Of DateTime), title As String)
        Me._id = id
        Me._createdOn = createdOn
        Me._title = title
    End Sub

    Public Property Id() As Integer
        Get
            Return _id
        End Get
        Set(ByVal value As Integer)
            _id = value
        End Set
    End Property

    Public Property CreatedOn() As Nullable(Of DateTime)
        Get
            Return _createdOn
        End Get
        Set(ByVal value As Nullable(Of DateTime))
            _createdOn = value
        End Set
    End Property

    Public Property Title() As String
        Get
            Return _title
        End Get
        Set(ByVal value As String)
            _title = value
        End Set
    End Property
End Class

Workaround: use a TypeConverter

Sub New()
    InitializeComponent()

    Dim items As New List(Of Item)

    items.Add(New Item(1, DateTime.Now.AddDays(2), "Item1"))
    items.Add(New Item(2, Nothing, "Item2"))
    items.Add(New Item(3, DateTime.Now.AddDays(4), "Item3"))
    items.Add(New Item(4, DateTime.Now.AddDays(5), "Item4"))

    Me.RadGridView1.DataSource = items
    Me.RadGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill
    DirectCast(Me.RadGridView1.Columns(1), GridViewDateTimeColumn).DataTypeConverter=New NullableDateTimeConverter()
End Sub

Public Class NullableDateTimeConverter
Inherits TypeConverter
   
    Public Overrides Function CanConvertFrom(ByVal context As ITypeDescriptorContext, ByVal sourceType As Type) As Boolean
        Return sourceType.Equals(GetType(String))
    End Function

    Public Overrides Function ConvertFrom(ByVal context As ITypeDescriptorContext, ByVal culture As CultureInfo, ByVal value As Object) As Object
        Dim parsedDate As DateTime
        If DateTime.TryParse(value.ToString(), parsedDate) Then
            Return parsedDate
        End If 
        Return Nothing
    End Function
End Class

Public Class Item
    Private _id As Integer
    Private _createdOn As Nullable(Of DateTime)
    Private _title As String

    Public Sub New(id As Integer, createdOn As Nullable(Of DateTime), title As String)
        Me._id = id
        Me._createdOn = createdOn
        Me._title = title
    End Sub

    Public Property Id() As Integer
        Get
            Return _id
        End Get
        Set(ByVal value As Integer)
            _id = value
        End Set
    End Property

    Public Property CreatedOn() As Nullable(Of DateTime)
        Get
            Return _createdOn
        End Get
        Set(ByVal value As Nullable(Of DateTime))
            _createdOn = value
        End Set
    End Property

    Public Property Title() As String
        Get
            Return _title
        End Get
        Set(ByVal value As String)
            _title = value
        End Set
    End Property
End Class

After a couple clicks, grid's context menu becomes unresponsive when using RadGridView through remote connection and Windows 7

The events are fired in the following order: UserAddingRow, EditorRequired, UserAddedRow eventfired when the new is pinned at the bottom and TAB key is processed.

Workaround:

public class FixGridNewRowBehavior : GridNewRowBehavior
{
    protected override bool ProcessTabKey(System.Windows.Forms.KeyEventArgs keys)
        {
            bool isInEditMode = this.EditorManager.IsInEditMode;
 
 
            if (isInEditMode)
            {
                IGridNavigator navigator = GridViewElement.Navigator;
 
                bool isLeftNavigation = navigator.IsFirstColumn(GridViewElement.CurrentColumn) && keys.Shift;
                bool isRightNavigation = navigator.IsLastColumn(GridViewElement.CurrentColumn) && !keys.Shift;
 
                if (isLeftNavigation || isRightNavigation)
                {
                    this.GridViewElement.EndEdit();
                }
 
                if (isLeftNavigation)
                {
                    navigator.SelectLastColumn();
                }
                else if (isRightNavigation)
                {
                    navigator.SelectFirstColumn();
                }
 
                if (isLeftNavigation || isRightNavigation)
                {
                    GridViewElement.BeginEdit();
                    return true;
                }
            }
 
            return base.ProcessTabKey(keys);
        }
} 

BaseGridBehavior gridBehavior = this.radGridView1.GridBehavior as BaseGridBehavior;
gridBehavior.UnregisterBehavior(typeof(GridViewNewRowInfo));
gridBehavior.RegisterBehavior(typeof(GridViewNewRowInfo), new FixGridNewRowBehavior());

To reproduce:

Sub New()
    InitializeComponent()

    Dim dt As New DataTable()
    dt.Columns.Add("Name", GetType(String))
    dt.Columns.Add("Price", GetType(Decimal))
    dt.Columns.Add("Id", GetType(Integer))
    dt.Columns.Add("ActivatedOn", GetType(DateTime))
    For i As Integer = 0 To 4
        dt.Rows.Add("Item" & i, i * 0.25, i, DateTime.Now.AddHours(i))
    Next
    Me.RadGridView1.DataSource = dt
    Me.RadGridView1.Columns("Id").[ReadOnly] = True
    Me.RadGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill
    AddHandler Me.RadGridView1.DefaultValuesNeeded, AddressOf radGridView1_DefaultValuesNeeded
    Me.RadGridView1.NewRowEnterKeyMode = RadGridViewNewRowEnterKeyMode.EnterMovesToLastAddedRow
End Sub
Private Sub radGridView1_DefaultValuesNeeded(sender As Object, e As GridViewRowEventArgs)
    e.Row.Cells("Id").Value = Me.radGridView1.Rows.Count
    e.Row.Cells("ActivatedOn").Value = DateTime.Now
End Sub

Select the read-only cell inside the new row and press Enter. You will notice that two duplicated rows are added.

Workaround: handle the RadGridView.PreviewKeyDown event and change the current  column to one that is not read-only

 AddHandler Me.RadGridView1.PreviewKeyDown, AddressOf GridPreviewKeyDown

 Private Sub GridPreviewKeyDown(sender As Object, e As PreviewKeyDownEventArgs)
        If e.KeyCode = Keys.Enter Then
            Me.RadGridView1.CurrentColumn = Me.RadGridView1.Columns(0)
            Me.RadGridView1.BeginEdit()
        End If
    End Sub 

1. Create a new project with RadGridView and setup 2 level hierarchy.
2. Add a checkbox column at the second level and set its pinned state to Left.
3. Run the application.
4. Expand the first row and click on the checkbox. Be sure that RadGridView contains enough columns in its child view to show horizontal scrollbar.

Workaround:  create a custom view definition
public class CustomTableViewDefinition : TableViewDefinition
{
    public override IRowView CreateViewUIElement(GridViewInfo viewInfo)
    {
        CustomTableElement table = new CustomTableElement();
        return table;
    }
}
 
public class CustomTableElement : GridTableElement
{
    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(GridTableElement);
        }
    }
 
    public override bool EnsureCellVisible(GridViewRowInfo rowInfo, GridViewColumn column)
    {
        if (column.IsPinned)
        {
            return true;
        }
        return base.EnsureCellVisible(rowInfo, column);
    }
}

Set the view definition to the child template by using the ViewDefinition property

this.gridViewDemoData.Templates[0].ViewDefinition = new CustomTableViewDefinition();

To reproduce:
- Set the first column header text to "+R/S";
- Export the grid with spread export.

Workaround:
class MySpreadExportRenderer : SpreadExportRenderer
{
    public override void SetCellSelectionValue(string text)
    {
        if (text == "+R/S")
        {
            var cellSelection = typeof(SpreadExportRenderer).GetField("cellSelection", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(this) as CellSelection;
            CellRange range = cellSelection.CellRanges.ElementAtOrDefault(0);

            CellValueFormat cvf = new CellValueFormat("@");

            var worksheet = typeof(SpreadExportRenderer).GetField("worksheet", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(this) as Worksheet;
            worksheet.Cells[range.FromIndex.RowIndex, range.FromIndex.ColumnIndex].SetFormat(cvf);
        }
        base.SetCellSelectionValue(text);
    }
}

Workaround: Use a custom editor and override IsModified method: 
class MyEditor : RadDropDownListEditor 
{
 public override bool IsModified 
{
 get 
{
 return true; 
}
 }
 }

 void radGridViewFilter_EditorRequired(object sender, EditorRequiredEventArgs e) 
{
 if (e.EditorType == typeof(RadDropDownListEditor)) { e.Editor = new MyEditor(); 
}
}

Workaround the issue by using the DataBindingComplete event in the following manner:

private GridViewRowInfo oldCurrentRow = null;

protected override void OnLoad(EventArgs e)
{
this.radGridView1.DataBindingComplete += this.OnDataBindingComplete;

this.oldCurrentRow = this.radGridView1.CurrentRow;
this.radGridView1.DataSource = Telerik.Help.Data.GetDummyEmployees(0);
}

private void OnDataBindingComplete(object sender, Telerik.WinControls.UI.GridViewBindingCompleteEventArgs e)
{
    if (this.oldCurrentRow != this.radGridView1.CurrentRow && this.radGridView1.RowCount == 0)
    {
        this.radGridView1.MasterTemplate.EventDispatcher.RaiseEvent<CurrentRowChangedEventArgs>(EventDispatcher.CurrentRowChanged,
            this.radGridView1.MasterTemplate, new CurrentRowChangedEventArgs(null, null));
    }
 
    this.oldCurrentRow = null;
}

To reproduce:
- add a grid to the form and use the following code for its setup:
            radGridView2.Columns.Add("ID");
            radGridView2.Columns.Add("Title");
            radGridView2.MultiSelect = true;
            radGridView2.Columns[0].SortOrder = RadSortOrder.Ascending;
            radGridView2.ReadOnly = true;

            radGridView2.BeginUpdate();
            for (int i = 0; i < 5; i++)
            {
                GridViewDataRowInfo row = new GridViewDataRowInfo(radGridView2.MasterTemplate.MasterViewInfo);
                row.Cells["ID"].Value = i;
                row.Cells["Title"].Value = "Title " + i;
                radGridView2.Rows.Add(row);
            }
            radGridView2.EndUpdate(true);

            radGridView2.Rows[0].IsCurrent = true;
            radGridView2.Rows[0].IsSelected= true;

- Once the application is started, hold down the shift key and click the third row in the grid 

Expected result: the first three rows are selected
Actual result: the last three rows are selected

WORKAROUND:
Use the BeginUpdate and EndUpdate methods of the TableElement, not the control:
radGridView2.TableElement.BeginUpdate();
//add rows
radGridView2.TableElement.EndUpdate(true);

To reproduce: bind the grid to self reference data source, and on a button click, Fill the TableAdapter

Workaround: clear the relations to clear the cache and add them back after the adapter is filled:
RadGridView1.Relations.Clear()
        Me.Table1TableAdapter.Fill(Me.Database8DataSet.Table1)
        Me.RadGridView1.Relations.AddSelfReference(Me.RadGridView1.MasterTemplate, "TaskID", "ParentTask")

The RadGridView is bound to DataView

Workaround: add row using the DataTable API:
private void radButton1_Click(object sender, EventArgs e)
{
    DataRow row = m_dvMat.Table.NewRow();
     row["Active"] = true;
     row["Category"] = form.m_sString;
     m_dvMat.Table.Rows.Add(row);
}

To reproduce:
Add a TabControl and two tabs. In the second tab add a RadGridView and in the Load event of the form set the SplitMode property of the grid. You will notice that it will not have effect until grouping or other similar action has been performed.

Workaround:
private void Form1_Load(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.Add("column1");
    dt.Columns.Add("column2");

    RadGridView1.DataSource = dt;

    this.RadGridView1.VisibleChanged += Visible_Changed;

}

private void Visible_Changed(object sender, EventArgs e)
{
    if (this.RadGridView1.Visible & !this.RadGridView1.SplitMode.Equals(Telerik.WinControls.UI.RadGridViewSplitMode.Horizontal)) {
        RadGridView1.SplitMode = Telerik.WinControls.UI.RadGridViewSplitMode.Horizontal;
    }
}

To reproduce:
Add a RadGridView and use the following code to populate it:
for (int i = 0; i < 15; i++)
{
    this.grid.Columns.Add(string.Format("Column {0}", i));
}

for (int i = 0; i < this.grid.Columns.Count * 15; i++)
{
    this.grid.Rows.AddNew();
}t
Set the theme to TelerikMetroTouch.
Scroll somewhere below the middle leave the scrollbar and leave the grid with the mouse. You will notice that the value of the scrollbar will change.

Workaround:
Subscribe to the RadPropertyChanging event of the TableElement:
RadGridView1.TableElement.RadPropertyChanging += Property_Changing;

void TableElement_RadPropertyChanging(object sender, RadPropertyChangingEventArgs args)
{
    args.Cancel = args.Property == GridTableElement.RowHeightProperty ||
                    args.Property == GridTableElement.TableHeaderHeightProperty ||
                    args.Property == GridTableElement.GroupHeaderHeightProperty ||
                    args.Property == GridTableElement.FilterRowHeightProperty;
}

To reproduce
- add Calculator column in the grid
- set the EnterKeyMode to EnterMovesToNextRow
- press enter when the cell is in edit mode.

Workaround:

-use custom GridDataRowBehavior like this:

class MyNewEnterBehavior : GridDataRowBehavior
{
    bool firstTime = true;
    protected override bool ProcessEnterKey(KeyEventArgs keys)
    {
        if (this.GridControl.IsInEditMode && this.GridControl.CurrentColumn is GridViewCalculatorColumn )
        {

            if (firstTime)
            {
                firstTime = false;
                return false;
            }
            firstTime = true;
            return base.ProcessEnterKey(keys); 
        }
        return base.ProcessEnterKey(keys);
    } 
}

In RadGridView with a TextBoxColumn.
  Set WrapText, Multiline and AcceptsReturn to true
  If  adding a new line, the return gives another new line instead of staying within the cell.

Workaround:
  Create a new behavior class:
//VB
Class MyNewRowBehavior
    Inherits GridNewRowBehavior
    Protected Overrides Function ProcessEnterKey(keys As KeyEventArgs) As Boolean
        If Me.GridControl.IsInEditMode AndAlso Me.GridControl.CurrentColumn.Name = "TextBoxColumn" Then
            Dim editor As RadTextBoxEditor = TryCast(Me.GridControl.ActiveEditor, RadTextBoxEditor)
            Dim element As RadTextBoxEditorElement = DirectCast(editor.EditorElement, RadTextBoxEditorElement)

            element.Text.Insert(element.Text.Length, Environment.NewLine)
            Return True
        Else
            Return MyBase.ProcessEnterKey(keys)
        End If
    End Function
End Class

//C#
class MyNewRowBehavior : GridNewRowBehavior
{
    protected override bool ProcessEnterKey(KeyEventArgs keys)
    {
        if (this.GridControl.IsInEditMode && this.GridControl.CurrentColumn.Name == "TextBoxColumn")
        {
            RadTextBoxEditor editor = this.GridControl.ActiveEditor as RadTextBoxEditor;
            RadTextBoxEditorElement element = (RadTextBoxEditorElement)editor.EditorElement;

            element.Text.Insert(element.Text.Length, Environment.NewLine);
            return true;
        }
        else
        {
            return base.ProcessEnterKey(keys);
        }
    }
}

then unregister the old behavior and register the new one:
//VB
DirectCast(radGridView1.GridBehavior, BaseGridBehavior).UnregisterBehavior(GetType(GridViewNewRowInfo))
DirectCast(radGridView1.GridBehavior, BaseGridBehavior).RegisterBehavior(GetType(GridViewNewRowInfo), New MyNewRowBehavior())

//C#
((BaseGridBehavior)radGridView1.GridBehavior).UnregisterBehavior(typeof(GridViewNewRowInfo));
((BaseGridBehavior)radGridView1.GridBehavior).RegisterBehavior(typeof(GridViewNewRowInfo), new MyNewRowBehavior());

Steps to reproduce:
1) Add RadGridView control
2) Use GridViewDecimalColumn:

        DataTable customDataTable = new DataTable();
        sampleDataTable.Columns.Add("Column name", typeof(double));

3) Set the right-to-left property of the control to true:

        this.radGridView1.RightToLeft = System.Windows.Forms.RightToLeft.Yes;

4) Re-size the form manually until horizontal scroll-bar appears and you will notice that the left border is missing

Expected result: the left border of the GridRowHeaderCellElement is visible
Actual result: the left border of the GridRowHeaderCellElement is missing

Workaround:
this.radGridView1.ViewCellFormatting +=new CellFormattingEventHandler(radGridView1_ViewCellFormatting);
 
void radGridView1_ViewCellFormatting(object sender, CellFormattingEventArgs e)
{
    if (e.CellElement is GridRowHeaderCellElement)
    {
        e.CellElement.BorderLeftWidth = 3;
    }
}

To reproduce:

Add a RadGridView to a form, dont dock it. Use the following code to add the rows, columns and the definition:



this.Grid.Columns.Add("Old");
this.Grid.Columns.Add("New");

Start the application and you will see that you cannot scroll to the end, horizontally.



Workaround:

Use the following code on a button click or execute it in a timer a few millisecond after the form has loaded in order to update the scrollbar's maximum value accordingly:



int width = 0;
foreach (var col in this.Grid.Columns)
{
    width += col.Width;
}


this.Grid.TableElement.HScrollBar.Maximum = width - this.Grid.TableElement.HScrollBar.SmallChange - this.Grid.TableElement.RowHeaderColumnWidth;

How to reproduce: 
Public Class Form1
    Sub New()

        InitializeComponent()

        Dim col As New GridViewTextBoxColumn("Column1")
        Me.RadGridView1.Columns.Add(col)
    End Sub

    Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
        Dim sw As New Stopwatch
        sw.Start()

        Me.RadGridView1.Rows.Clear()
        Me.RadGridView1.BeginUpdate()
        Dim RowInfo
        For ii = 1 To 100000
            RowInfo = Me.RadGridView1.Rows.AddNew
            RowInfo.Cells("Column1").Value = ii
        Next
        Me.RadGridView1.EndUpdate()

        sw.Stop()
        Console.WriteLine("Elapsed: " & sw.Elapsed.TotalSeconds)
    End Sub
End Class

Workaround: add data to a collection and use bound mode