Please find attached a sample project.

1. Select the new row and activate te editor.
2. Do not enter any value and click outside the new row. The exception is thrown.

Workaround: bind directly to the query result:
this.radGridView1.DataSource = (from p in context.Customers select p).ToList();

Workaround: instead of using the default alternating row color for the mentioned themes, use the override theme setting in the CellFormatting event: http://www.telerik.com/help/winforms/tpf-override-theme-settings-at-run-time.html
private void radGridView1_CellFormatting(object sender, CellFormattingEventArgs e)
{
    if (e.Row is GridViewDataRowInfo)
    {
        if (e.RowIndex % 2 == 0)
        {
            e.CellElement.SetThemeValueOverride(LightVisualElement.BackColorProperty, Color.Red, "");
            e.CellElement.SetThemeValueOverride(LightVisualElement.DrawFillProperty, true, "");
            e.CellElement.SetThemeValueOverride(LightVisualElement.GradientStyleProperty, GradientStyles.Solid, "");
        }
        else
        {
            e.CellElement.ResetThemeValueOverride(LightVisualElement.BackColorProperty, "");
            e.CellElement.ResetThemeValueOverride(LightVisualElement.DrawFillProperty, "");
            e.CellElement.ResetThemeValueOverride(LightVisualElement.GradientStyleProperty, ""); 
        }
    }
}

Currently the Paging functionality does not support server side operations. It should be extended to support them, e.g. with EntityFramework and Telerik Data Access

To reproduce:
Search a specific text by focusing the search box programmatically and the using the SendKeys method:
private void radButton1_Click(object sender, EventArgs e)
{
    GridSearchCellElement searchCell = radGridView1.TableElement.GetCellElement(radGridView1.MasterView.TableSearchRow, null) as GridSearchCellElement;
    if (searchCell != null)
    {
        searchCell.SearchTextBox.Focus();
        searchCell.SearchTextBox.Text = string.Empty;
        SendKeys.Send("t");
        SendKeys.Send("e");
        SendKeys.Send("s");
        SendKeys.Send("t");
    }
}

Workaround: 
Repeat the search in the SearchProgressChanged event:

radGridView1.MasterView.TableSearchRow.SearchProgressChanged += TextationSearchProgressHandler;

protected void TextationSearchProgressHandler(object sender, SearchProgressChangedEventArgs e)
{
    if (e.SearchFinished && null != radGridView1.TableElement)
    {
        GridSearchCellElement searchCell = radGridView1.TableElement.GetCellElement(radGridView1.MasterView.TableSearchRow, null) as GridSearchCellElement;
        if (searchCell != null
             && searchCell.SearchTextBox.TextBoxItem.Text != e.SearchCriteria)
        {
            radGridView1.MasterView.TableSearchRow.Search(searchCell.SearchTextBox.TextBoxItem.Text);
        }
    }
}

To reproduce:

public Form1() 
{
    InitializeComponent();

    DataTable dt = new DataTable();
    for (int i = 0; i < 5; i++)
    {
        dt.Columns.Add("Col"+i);
    }
    for (int i = 0; i < 2000; i++)
    {
        DataRow row = dt.NewRow();
        foreach (DataColumn col in dt.Columns)
        {
            row[col.ColumnName] = "Data" + i + "." + dt.Columns.IndexOf(col);
        }
        dt.Rows.Add(row);
    }
    this.radGridView1.DataSource = dt;
    this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;
}

private void radButton1_Click(object sender, EventArgs e)
{
    RadPrintPreviewDialog dialog = new RadPrintPreviewDialog();
    dialog.Document = this.radPrintDocument1;
    dialog.ShowDialog();
}

Workaround: this.radGridView1.AutoSizeRows = true;

To reproduce: use the following code snippet. You will notice that the "Accounting Manager" group is missing.

private void Form1_Load(object sender, EventArgs e)
{ 
    this.customersTableAdapter.Fill(this.nwindDataSet.Customers);

    this.radGridView1.DataSource = this.customersBindingSource;

    ColumnGroupsViewDefinition view = new ColumnGroupsViewDefinition();
    view.ColumnGroups.Add(new GridViewColumnGroup("Customer Contact"));
    view.ColumnGroups.Add(new GridViewColumnGroup("Details"));
    view.ColumnGroups[1].Groups.Add(new GridViewColumnGroup("Address"));
    view.ColumnGroups[1].Groups.Add(new GridViewColumnGroup("Contact"));
    view.ColumnGroups[0].Rows.Add(new GridViewColumnGroupRow());
    view.ColumnGroups[0].Rows[0].ColumnNames.Add("CompanyName");
    view.ColumnGroups[0].Rows[0].ColumnNames.Add("ContactName");
    view.ColumnGroups[0].Rows[0].ColumnNames.Add("ContactTitle");
    view.ColumnGroups[1].Groups[0].Rows.Add(new GridViewColumnGroupRow());
    view.ColumnGroups[1].Groups[0].Rows[0].ColumnNames.Add("Address");
    view.ColumnGroups[1].Groups[0].Rows[0].ColumnNames.Add("City");
    view.ColumnGroups[1].Groups[0].Rows[0].ColumnNames.Add("Country");
    view.ColumnGroups[1].Groups[1].Rows.Add(new GridViewColumnGroupRow());
    view.ColumnGroups[1].Groups[1].Rows[0].ColumnNames.Add("Phone");
    view.ColumnGroups[1].Groups[1].Rows[0].ColumnNames.Add("Fax");
    radGridView1.ViewDefinition = view;

    GroupDescriptor descriptor = new GroupDescriptor();
    descriptor.GroupNames.Add("ContactTitle", ListSortDirection.Ascending);
    this.radGridView1.GroupDescriptors.Add(descriptor);

    this.radGridView1.Groups[0].GroupRow.IsPinned = true;
}

Please refer to the attached screenshot and sample video.

Workaround:
public class CustomGrid : RadGridView
{
    public override string ThemeClassName  
    { 
        get 
        { 
            return typeof(RadGridView).FullName;  
        }
    }

    protected override void OnKeyPress(KeyPressEventArgs e)
    {
        this.BeginEdit();
        if (this.GridViewElement.ActiveEditor is RadDropDownListEditor)
        {
            string symbol = e.KeyChar.ToString();
            RadDropDownListEditor editor = this.GridViewElement.ActiveEditor as RadDropDownListEditor;
            RadDropDownListEditorElement element = editor.EditorElement as RadDropDownListEditorElement;

            if ((element.AutoCompleteMode & AutoCompleteMode.Suggest) == AutoCompleteMode.Suggest)
            {
                element.EditableElementText += symbol;
                element.EditableElement.SelectionStart = 1;
                element.EditableElement.SelectionLength = 0;
            }
        }
        base.OnKeyPress(e);
    }
}

To reproduce:

private void Form1_Load(object sender, EventArgs e)
{
    this.productsTableAdapter.Fill(this.nwindDataSet.Products);
    this.categoriesTableAdapter.Fill(this.nwindDataSet.Categories);
    
    radGridView1.AllowSearchRow = true;
    radGridView1.DataSource = nwindDataSet.Categories;
    radGridView1.MasterTemplate.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
    radGridView1.UseScrollbarsInHierarchy = true;

    GridViewTemplate template = new GridViewTemplate();
    template.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
    template.DataSource = nwindDataSet.Products;
    radGridView1.MasterTemplate.Templates.Add(template);

    GridViewRelation relation = new GridViewRelation(radGridView1.MasterTemplate);
    relation.ChildTemplate = template;
    relation.RelationName = "CategoriesProducts";
    relation.ParentColumnNames.Add("CategoryID");
    relation.ChildColumnNames.Add("CategoryID");
    radGridView1.Relations.Add(relation); 
}

Workaround:
private void radGridView1_CurrentRowChanged(object sender, CurrentRowChangedEventArgs e)
{
    if (this.radGridView1.CurrentRow != null)
    {
        if (this.radGridView1.CurrentRow.HierarchyLevel > 0)
        {
            tableElement.ScrollToRow((GridViewHierarchyRowInfo)(this.radGridView1.CurrentRow).Parent);
             this.radGridView1.TableElement.EnsureRowVisible((GridViewHierarchyRowInfo)(this.radGridView1.CurrentRow).Parent);
            tableElement.ScrollToRow(this.radGridView1.CurrentRow);
            tableElement.EnsureRowVisible(this.radGridView1.CurrentRow);
        }
    }
}

To reproduce: use the following code snippet. From the filtering box, when you select "Null" and then select "All", the following error occurs:
Item has already been added. Key in dictionary: '(Blanks)'  Key being added: '(Blanks)'

DataTable dt = new DataTable();
dt.Columns.Add("Id", typeof(int));
dt.Columns.Add("Name", typeof(string));

dt.Rows.Add(1,"A");
dt.Rows.Add(2, "");
dt.Rows.Add(3, null);
dt.Rows.Add(4, "B");
dt.Rows.Add(5, "C");
dt.Rows.Add(6, "");
this.radGridView1.DataSource = dt;
this.radGridView1.AutoSizeColumnsMode = Telerik.WinControls.UI.GridViewAutoSizeColumnsMode.Fill;
this.radGridView1.EnableFiltering = true;
this.radGridView1.ShowFilteringRow = false;
this.radGridView1.ShowHeaderCellButtons = true;

Workaround:  this.radGridView1.FilterPopupInitialized += radGridView1_FilterPopupInitialized;

RadListFilterDistinctValuesTable selectedValues;

private void radGridView1_FilterPopupInitialized(object sender, Telerik.WinControls.UI.FilterPopupInitializedEventArgs e)
{
    RadListFilterPopup popup = e.FilterPopup as RadListFilterPopup;
    selectedValues = popup.MenuTreeElement.SelectedValues;
    popup.MenuTreeElement.TreeView.NodeCheckedChanged += TreeView_NodeCheckedChanged;
}

private void TreeView_NodeCheckedChanged(object sender, TreeNodeCheckedEventArgs e)
{
    if (e.Node.CheckState == Telerik.WinControls.Enumerations.ToggleState.Off)
    {
        if (selectedValues.Contains(e.Node.Text))
        {
            selectedValues.Remove(e.Node.Text);
        }
    }
}

Workaround: use a custom BaseGridBehavior

public Form1()
{
    InitializeComponent();

    this.radGridView1.GridBehavior = new MyBaseGridBehavior();
}

public class MyBaseGridBehavior : BaseGridBehavior
{
    public override bool ProcessKey(KeyEventArgs keys)
    {
        if (keys.Control && this.GridControl.CurrentColumn == null)
        {
            return false;
        }

        return base.ProcessKey(keys);
    }
}

Add a Card view layout.

To reproduce:
radGridView1.GridNavigator.SelectFirstRow();
for (int i = 0; i < radGridView1.RowCount; i++)
{
    var result = radGridView1.GridNavigator.SelectNextRow(1);
}

Workaround:
- Move to the last row first:
radGridView1.GridNavigator.SelectLastRow();

Workaround: suspend columns notifications when preview dropping and resume the notification after the drag drop service has stopped:

Dim svc As RadDragDropService = Me.RadGridView1.GridViewElement.GetService(Of RadDragDropService)()
AddHandler svc.Stopped, svc_Stopped
AddHandler svc.PreviewDragDrop, AddressOf svc_PreviewDragDrop

Private Sub svc_PreviewDragDrop(sender As Object, e As RadDropEventArgs)
    For Each col As GridViewColumn In Me.RadGridView1.Columns
        col.SuspendPropertyNotifications()
    Next
End Sub

Private Function svc_Stopped() As Object
    For Each col As GridViewColumn In Me.RadGridView1.Columns
        col.ResumePropertyNotifications()
    Next
End Function

To reproduce:

public Form1()
{
    InitializeComponent();
    BindingList<Item> items = new BindingList<Item>();
    
    for (int i = 0; i < 30; i++)
    {
        if (i % 3 == 0)
        {
            items.Add(new Item(i,"Item" + i, IndeterminateBoolean.YesAndNo));
        }
        else if (i % 3 == 1)
        {
            items.Add(new Item(i, "Item" + i, IndeterminateBoolean.Yes));
        }
        else
        {
            items.Add(new Item(i, "Item" + i, IndeterminateBoolean.No));
        }
    }
    this.radGridView1.DataSource = items;
    GridViewCheckBoxColumn checkBox = new GridViewCheckBoxColumn("CheckBoxCol");
    checkBox.DataTypeConverter = new IndeterminateBooleanToggleStateConverter();
    checkBox.FieldName = "IsActive";
    checkBox.ThreeState = true;
    this.radGridView1.Columns.Add(checkBox);
    this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
    this.radGridView1.EnableFiltering = true;

    this.radGridView1.ShowHeaderCellButtons = true;
    this.radGridView1.ShowFilteringRow = false;
}

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

    public string Name { get; set; }

    public IndeterminateBoolean IsActive { get; set; }

    public Item(int id, string name, IndeterminateBoolean isActive)
    {
        this.Id = id;
        this.Name = name;
        this.IsActive = isActive;
    }
}

public enum IndeterminateBoolean
{
    No,
    Yes,
    YesAndNo
}

public class IndeterminateBooleanToggleStateConverter : TypeConverter
{
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        return sourceType == typeof(ToggleState);
    }
    
    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
    {
        return destinationType == typeof(ToggleState);
    }

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        if (value is ToggleState)
        {
            switch ((ToggleState)value)
            {
                case ToggleState.On:
                    return IndeterminateBoolean.Yes;
                case ToggleState.Off:
                    return IndeterminateBoolean.No;
                case ToggleState.Indeterminate:
                default:
                    return IndeterminateBoolean.YesAndNo;
            }
        }
        else
        {
            return base.ConvertFrom(context, culture, value);
        }
    }
    
    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
    {
        if (destinationType == typeof(ToggleState))
        {
            if (value is IndeterminateBoolean)
            {
                switch ((IndeterminateBoolean)value)
                {
                    case IndeterminateBoolean.Yes:
                        return ToggleState.On;
                    case IndeterminateBoolean.No:
                        return ToggleState.Off;
                    case IndeterminateBoolean.YesAndNo:
                    default:
                        return ToggleState.Indeterminate;
                }
            }
            if (value is string)
            {
                switch (((string)value ?? string.Empty).Trim())
                {
                    case "Yes":
                        return ToggleState.On;
                    case "No":
                    case "":
                        return ToggleState.Off;
                    case "Both":
                    default:
                        return ToggleState.Indeterminate;
                }
            }
            else
            {
                return base.ConvertTo(context, culture, value, destinationType);
            }
        }
        else
        {
            return base.ConvertTo(context, culture, value, destinationType);
        }
    }
}

Workaround: use the custom filtering functionality: http://docs.telerik.com/devtools/winforms/gridview/filtering/custom-filtering

You can access the RadGridView.FilterDescriptors collection and according to the FilterDescriptor.Expression property to determine whether the row will be visible or not. 

To reproduce:

public Form1()
{
    InitializeComponent();
    BindingList<Item> items = new BindingList<Item>();
    
    for (int i = 0; i < 30; i++)
    {
        if (i % 3 == 0)
        {
            items.Add(new Item(i,"Item" + i, IndeterminateBoolean.YesAndNo));
        }
        else if (i % 3 == 1)
        {
            items.Add(new Item(i, "Item" + i, IndeterminateBoolean.Yes));
        }
        else
        {
            items.Add(new Item(i, "Item" + i, IndeterminateBoolean.No));
        }
    }
    this.radGridView1.DataSource = items;
    this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
    this.radGridView1.EnableFiltering = true; 
    this.radGridView1.ShowHeaderCellButtons = true;
    this.radGridView1.ShowFilteringRow = false; 
}

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

    public string Name { get; set; }

    public IndeterminateBoolean IsActive { get; set; }

    public Item(int id, string name, IndeterminateBoolean isActive)
    {
        this.Id = id;
        this.Name = name;
        this.IsActive = isActive;
    }
}

public enum IndeterminateBoolean
{
    No,
    Yes,
    YesAndNo
}

Workaround: use custom filtering http://docs.telerik.com/devtools/winforms/gridview/filtering/custom-filtering

To reproduce:
Add the following view:
for (int i = 0; i < 8; i++)
{
    radGridView2.Columns.Add("Col" + (i+1));
}

ColumnGroupsViewDefinition view = new ColumnGroupsViewDefinition();
view.ColumnGroups.Add(new GridViewColumnGroup("G1"));
view.ColumnGroups.Add(new GridViewColumnGroup("G2"));
view.ColumnGroups.Add(new GridViewColumnGroup("G3"));

view.ColumnGroups[0].Rows.Add(new GridViewColumnGroupRow());
view.ColumnGroups[0].Rows[0].ColumnNames.Add("Col1");
view.ColumnGroups[0].Rows[0].ColumnNames.Add("Col2");
view.ColumnGroups[0].Rows[0].ColumnNames.Add("Col3");

view.ColumnGroups[1].Rows.Add(new GridViewColumnGroupRow());
view.ColumnGroups[1].Rows[0].ColumnNames.Add("Col4");
view.ColumnGroups[1].Rows[0].ColumnNames.Add("Col5");

view.ColumnGroups[2].Rows.Add(new GridViewColumnGroupRow());
view.ColumnGroups[2].Rows[0].ColumnNames.Add("Col6");
view.ColumnGroups[2].Rows[0].ColumnNames.Add("Col7");
view.ColumnGroups[2].Rows[0].ColumnNames.Add("Col8");

radGridView2.ViewDefinition = view;

for (int i = 0; i < 10; i++)
{
    radGridView2.Rows.Add("row"+i, "test","test","test","test","test","test");
}


radGridView2.Columns[2].IsVisible = false;
radGridView2.Columns[7].IsVisible = false;

- Then export the grid with the spread exporter.

When the RadGridView.EnabledPaging property is set to true, the user should be allowed to specify not only the PageSize,but also the PagesCount for example. Afterwards, it would be convenient to have an event similar to RowSourceNeeded in order to load pages data on demand.

To reproduce:

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Me.RadGridView1.AutoGenerateColumns = False

    Dim column = New GridViewTextBoxColumn
    column.Name = "Name"
    column.FieldName = "ChildItem"
    column.DataType = GetType(CustomItem)
    column.DataTypeConverter = New CustomItemTypeConverter()

    Me.RadGridView1.Columns.Add(column)
    Me.RadGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill

    Dim objects =
        {
            New CustomContainer With {.ChildItem = New CustomItem With {.Name = "A"}},
            New CustomContainer With {.ChildItem = New CustomItem With {.Name = "B"}},
            New CustomContainer With {.ChildItem = New CustomItem With {.Name = "C"}}
        }

    Me.RadGridView1.DataSource = objects
End Sub

Private Sub RadGridView_EditorRequired(sender As Object, e As EditorRequiredEventArgs) Handles RadGridView1.EditorRequired
    e.EditorType = GetType(GridSpinEditor)
End Sub

Class CustomContainer
    Public Property ChildItem As CustomItem
End Class

Class CustomItem
    Public Property Name As String
End Class

Class CustomItemTypeConverter
Inherits TypeConverter

    Public Overrides Function CanConvertFrom(context As ITypeDescriptorContext, sourceType As Type) As Boolean
        If sourceType = GetType(Decimal) Then
            Return True
        End If

        Return MyBase.CanConvertFrom(context, sourceType)
    End Function

    Public Overrides Function CanConvertTo(context As ITypeDescriptorContext, destinationType As Type) As Boolean
        If destinationType = GetType(Decimal) OrElse destinationType = GetType(String) OrElse destinationType = GetType(CustomItem) Then
            Return True
        End If

        Return MyBase.CanConvertTo(context, destinationType)
    End Function

    Public Overrides Function ConvertTo(context As ITypeDescriptorContext, culture As System.Globalization.CultureInfo, _
                                        value As Object, destinationType As Type) As Object
        If TypeOf value Is CustomItem Then
            Dim customValue = DirectCast(value, CustomItem)

            If destinationType = GetType(Decimal) Then
                Return Microsoft.VisualBasic.AscW(customValue.Name.Chars(0))
            ElseIf destinationType = GetType(String) Then
                Return customValue.Name
            ElseIf destinationType = GetType(CustomItem) Then
                Return customValue
            Else
                Return MyBase.ConvertTo(context, culture, value, destinationType)
            End If
        End If

        Return MyBase.ConvertTo(context, culture, value, destinationType)
    End Function

    Public Overrides Function ConvertFrom(context As ITypeDescriptorContext, culture As System.Globalization.CultureInfo, value As Object) As Object
        If TypeOf value Is Decimal Then
            Dim decValue = DirectCast(value, Decimal)
            Dim intValue = CInt(decValue)
            Dim charValue = Microsoft.VisualBasic.ChrW(intValue)

            Return New CustomItem With {.Name = New String(charValue, 1)}
        End If

        Return MyBase.ConvertFrom(context, culture, value)
    End Function

End Class


Workaround:

Public Class MyEditor
    Inherits GridSpinEditor

    Public Overrides ReadOnly Property IsModified() As Boolean
        Get
            If Me.originalValue Is Nothing Then
                Return (Me.Value IsNot Nothing AndAlso Me.Value <> DBNull.Value)
            End If

            If Me.Value Is Nothing Then
                Return (Me.originalValue IsNot Nothing AndAlso Me.originalValue <> DBNull.Value)
            End If
            Dim column As GridViewDataColumn = (DirectCast(Me.OwnerElement, GridDataCellElement)).ColumnInfo
            If column.DataTypeConverter IsNot Nothing AndAlso column.DataTypeConverter.CanConvertTo(Me.OwnerElement, GetType(Decimal)) Then
                Return Not column.DataTypeConverter.ConvertTo(Me.OwnerElement, column.FormatInfo, Me.originalValue, GetType(Decimal)).Equals(Convert.ToDecimal(Me.Value))
            End If

            Return Not Convert.ToDecimal(Me.originalValue).Equals(Convert.ToDecimal(Me.Value))
        End Get
    End Property
End Class


Private Sub RadGridView_EditorRequired(sender As Object, e As EditorRequiredEventArgs) Handles RadGridView1.EditorRequired
    e.EditorType = GetType(MyEditor)
End Sub

To reproduce:
- Add an expression column with nullable type as a data source. 
- Open the property builder.

Workaround: 
Set the data type at run time. 

If a dock window is focused programmatically, the RowValidating event is fired before selecting the new row by mouse cursor.