If current culture uses comma as delimeter, the MS Excel cannot handle the decimal values in a right way.

To reproduce: the issue is reproducible in the Demo application >> GridView >> Tabbed Views. Follow the steps from the gif file.

Workaround:     
    private void radGridView1_ViewCellFormatting(object sender, CellFormattingEventArgs e)
        {
            GridDetailViewCellElement cell = e.CellElement as GridDetailViewCellElement;
            if (cell != null)
            {
                cell.MinSize = new Size(e.CellElement.Parent.Size.Width - this.radGridView1.TableElement.GroupIndent , 10);
            }
        }

How to reproduce: check the code snippet below and the attached video. 
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        this.SetupGrid();

        this.radGridView1.Dock = DockStyle.Fill;
        this.radGridView1.UseScrollbarsInHierarchy = true;
    }

    private void SetupGrid()
    {
        BindingList<Teacher> teachers = new BindingList<Teacher>();
        BindingList<Student> students = new BindingList<Student>();

        for (int i = 1; i <= 2; i++)
        {
            teachers.Add(new Teacher
            {
                TeacherId = i,
                TeacherFirstName = "FirstName " + i,
                TeacherLastName = "FirstName " + i,

            });

            for (int j = 1; j <= 3; j++)
            {
                students.Add(new Student
                {
                    SudentId = j,
                    TeacherId = i,
                    SudentFirstName = "Student " + j,
                    SudentLastName = "LastName " + j,

                });
            }
        }

        this.radGridView1.Templates.Clear();
        this.radGridView1.DataSource = null;

        this.radGridView1.DataSource = teachers;
        this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

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

        GridViewRelation relation = new GridViewRelation(radGridView1.MasterTemplate);
        relation.ChildTemplate = template;
        relation.RelationName = "TeacherStudents";
        relation.ParentColumnNames.Add("TeacherId");
        relation.ChildColumnNames.Add("TeacherId");
        this.radGridView1.Relations.Add(relation);

        this.radGridView1.ChildViewExpanded += RadGridView1_ChildViewExpanded1;
    }

    private void RadGridView1_ChildViewExpanded1(object sender, ChildViewExpandedEventArgs e)
    {
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        this.radGridView1.SaveLayout("..\\..\\save.xml");
    }

    private void radButton2_Click(object sender, EventArgs e)
    {
        this.radGridView1.LoadLayout("..\\..\\save.xml");
    }
}

public class Teacher
{
    public int TeacherId { get; set; }

    public string TeacherFirstName { get; set; }

    public string TeacherLastName { get; set; }
}

public class Student
{
    public int SudentId { get; set; }

    public int TeacherId { get; set; }

    public string SudentFirstName { get; set; }

    public string SudentLastName { get; set; }
}


Workaround: prevent the child templates from serializing
public class MyRadGridView : RadGridView
{
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadGridView).FullName;
        }
    }

    public override void SaveLayout(string fileName)
    {
        MyGridViewLayoutSerializer ser = new MyGridViewLayoutSerializer(this.XmlSerializationInfo);
        using (XmlTextWriter writer = new XmlTextWriter(fileName, Encoding.UTF8))
        {
            writer.Formatting = Formatting.Indented;
            writer.WriteStartElement("RadGridView");
            ser.WriteObjectElement(writer, this);
        }
    }
}

public class MyGridViewLayoutSerializer : GridViewLayoutSerializer
{
    public MyGridViewLayoutSerializer(ComponentXmlSerializationInfo componentSerializationInfo)
        : base(componentSerializationInfo)
    { }

    protected override bool ShouldSerializeValue(object component, PropertyDescriptor property, PropertySerializationMetadata overwriteMetadata)
    {
        if (property.Name == "Templates")
        {
            return false;
        }

        return base.ShouldSerializeValue(component, property, overwriteMetadata);
    }
}

To reproduce: use the following code snippet:

    Sub New()

        InitializeComponent()

        Dim view As 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 


    End Sub

    Private Sub RadForm1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.CustomersTableAdapter.Fill(Me.NwindDataSet.Customers)
        Me.RadGridView1.BestFitColumns(BestFitColumnMode.AllCells)

        RadGridView1.Columns("Fax").IsVisible = False
        RadGridView1.Columns("Phone").IsVisible = False
        
        Dim spreadExporter As GridViewSpreadExport = New GridViewSpreadExport(Me.RadGridView1)
        Dim exportRenderer As New SpreadExportRenderer()
        spreadExporter.HiddenColumnOption = Export.HiddenOption.ExportAsHidden
        spreadExporter.FreezeHeaderRow = True
        spreadExporter.ExportGroupedColumns = True
        spreadExporter.ExportChildRowsGrouped = True
        spreadExporter.ExportVisualSettings = True
        spreadExporter.ExportHierarchy = True
        spreadExporter.ExportViewDefinition = True
        spreadExporter.ExportFormat = SpreadExportFormat.Xlsx
        Dim fileName = "..\..\export" & DateTime.Now.ToLongTimeString().Replace(":", "_") & ".xlsx"
        
        spreadExporter.RunExport(fileName, exportRenderer)
        Process.Start(fileName)
    End Sub

Workaround: instead of hiding all the columns inside a group, hide the entire group: 

    Sub New()

        InitializeComponent()

        Dim view As 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


        view.ColumnGroups(1).Groups.Last().IsVisible=False 


    End Sub

To reproduce:
- Use a column with numbers stored as strings.
- Set the data type to decimal
- The columns should be sorted according to the number value not alphabetically.

Workaround:
var col = new GridViewTextBoxColumn();
col.DataTypeConverter = new DecimalConverter();
col.FieldName = "Dosage";
col.UseDataTypeConverterWhenSorting = true;
col.DataType = typeof(decimal);
radGridView1.Columns.Add(col);

public class DecimalConverter : TypeConverter
{
    public override bool CanConvertTo(ITypeDescriptorContext context, Type destination_type)
    {
        
        if (destination_type == typeof(decimal))
        {
            return true;
        }

        return base.CanConvertTo(context, destination_type);
    }
    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destination_type)
    {
        if (destination_type == typeof(decimal))
        {
            return decimal.Parse(value.ToString());
        }

        return base.ConvertTo(context, culture, value, destination_type);
    }
}

Workaround:

        private void radGridView1_ConditionalFormattingFormShown(object sender, EventArgs e)
        {
            ConditionalFormattingForm f = sender as ConditionalFormattingForm;
            if (f != null)
            {
                RadPropertyGrid radPropertyGridProperties = f.Controls["radPropertyGridProperties"] as RadPropertyGrid; 
                radPropertyGridProperties.ItemFormatting += radPropertyGridProperties_ItemFormatting;
                  radPropertyGridProperties.ItemFormatting += radPropertyGridProperties_ItemFormatting;
            }
        }

        private void radPropertyGridProperties_ItemFormatting(object sender, PropertyGridItemFormattingEventArgs e)
        {
            if (e.Item.Label=="CellFont")
            {
                e.Item.Label = "aaa";
            }
        }

This can be used for large amounts of data.

Check this - https://docs.telerik.com/devtools/document-processing/libraries/radpdfprocessing/formats-and-conversion/pdf/pdfstreamwriter/pdfstreamwriter

The scenario which should be covered is selecting some data from Excel and pasting in the new row of RadGridView. This is an easy way for inserting data in the grid.

To reproduce: please refer to the attached screenshot

        public RadForm1()
        {
            InitializeComponent();

            ThemeResolutionService.ApplicationThemeName = "Fluent";

            this.BackColor = Color.White;
            this.radGridView1.EnableGrouping = false;
        }

Workaround: this.radGridView1.TableElement.Margin = new Padding(0, 1, 0, 0);

To reproduce: run the attached sample project and activate the editor for the cell. You will notice that the row's height is now adjusted and single line text is displayed. It seems that the issue occurs because of the set Font property of the grid.

Workaround:  
        private void RadGridView1_CellEditorInitialized(object sender, Telerik.WinControls.UI.GridViewCellEventArgs e)
        {
            e.Row.MinHeight = e.Row.Height + 3;
            RadTextBoxEditor tbEditor = e.ActiveEditor as RadTextBoxEditor;
            if (tbEditor != null)
            {
                tbEditor.Multiline = true;
            }
        }

        private void radGridView1_CellEndEdit(object sender, GridViewCellEventArgs e)
        {
            e.Row.MinHeight = 0; 
        }

A possible workaround is to use the following KB and change how it is implemented to iterate the MasterTemplate.Rows collection instead of the ViewInfo.Rows collection

https://www.telerik.com/support/kb/winforms/gridview/details/add-check-all-in-the-header-cell-for-a-gridviewcheckboxcolumn

To reproduce:
- Set IsSearchAsync to false.
- Search for something and press down arrow to navigate to the last found item.
- Press down again the selection is not moved to the first item.
 

Use attached to reproduce.

Workaround:
private void RadGridView1_UserAddingRow(object sender, GridViewRowCancelEventArgs e)
{
    e.Cancel = true;
}

Use attached to reproduce:
- Just search for something and you will notice that the waiting bar does not disappear. 

Workaround:
public RadForm1()
{
    InitializeComponent();

    
    radGridView1.MasterView.TableSearchRow.IsSearchAsync = false;
    radGridView1.MasterView.TableSearchRow.SearchProgressChanged += TableSearchRow_SearchProgressChanged;

}

private void TableSearchRow_SearchProgressChanged(object sender, SearchProgressChangedEventArgs e)
{
    var searchCell = radGridView1.TableElement.FindDescendant<GridSearchCellElement>();
    if (searchCell != null)
    {
        var waitingBar = searchCell.Children[1] as RadWaitingBarElement;
        waitingBar.StopWaiting();
        waitingBar.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
    }
}

How to reproduce:
public partial class Form1 : Form
{
    private RadGridView grid = new RadGridView();

    public Form1()
    {
        InitializeComponent();

        Controls.Add(grid);
        grid.Dock = DockStyle.Fill;
        grid.DataSource = this.GetData();
    }

    private object GetData()
    {
        DataTable dataTable = new DataTable();
        dataTable.Columns.Add("Id", typeof(int));
        dataTable.Columns.Add("Name", typeof(string));
        dataTable.Columns.Add("Checked", typeof(bool));

        for (int i = 0; i < 200; i++)
        {
            dataTable.Rows.Add(i, "Name " + i, i % 2 == 0);
        }

        return dataTable;
    }

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

        grid.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

        GridViewCheckBoxColumn checkBoxColumn = (GridViewCheckBoxColumn)grid.Columns["Checked"];
        checkBoxColumn.EnableHeaderCheckBox = true;
        checkBoxColumn.SortOrder = RadSortOrder.Ascending;
    }
}

Workaround: 
public partial class Form1 : Form
{
    private RadGridView grid = new RadGridView();

    public Form1()
    {
        InitializeComponent();

        Controls.Add(grid);
        grid.Dock = DockStyle.Fill;
        grid.DataSource = this.GetData();

        grid.MouseDown += grid_MouseDown;
        grid.MouseUp += grid_MouseUp;
    }

    private object GetData()
    {
        DataTable dataTable = new DataTable();
        dataTable.Columns.Add("Id", typeof(int));
        dataTable.Columns.Add("Name", typeof(string));
        dataTable.Columns.Add("Checked", typeof(bool));

        for (int i = 0; i < 200; i++)
        {
            dataTable.Rows.Add(i, "Name " + i, i % 2 == 0);
        }

        return dataTable;
    }

    private void grid_MouseDown(object sender, MouseEventArgs e)
    {
        RadGridView grid = (RadGridView)sender;
        RadCheckBoxElement cell = grid.ElementTree.GetElementAtPoint(e.Location) as RadCheckBoxElement;
        if (cell != null && cell.Parent is GridCheckBoxHeaderCellElement)
        {
            sw = new Stopwatch();
            sw.Start();
            grid.BeginUpdate();
        }
    }

    Stopwatch sw;
    private void grid_MouseUp(object sender, MouseEventArgs e)
    {
        RadGridView grid = (RadGridView)sender;
        RadCheckBoxElement cell = grid.ElementTree.GetElementAtPoint(e.Location) as RadCheckBoxElement;
        if (cell != null && cell.Parent is GridCheckBoxHeaderCellElement)
        {
            grid.EndUpdate();
            sw.Stop();
            Console.WriteLine(sw.ElapsedMilliseconds);
        }
    }

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

        grid.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;

        GridViewCheckBoxColumn checkBoxColumn = (GridViewCheckBoxColumn)grid.Columns["Checked"];
        checkBoxColumn.EnableHeaderCheckBox = true;
        checkBoxColumn.SortOrder = RadSortOrder.Ascending;
    }
}

Use attached to reproduce.
- Edit random cell and press Enter.
- Check the CellValueChanged event handler, the changes variable is null.

This will work if you comment the OnShown method.

Workaround:
IEditableObject editbaleObject = radGridView1.CurrentRow.DataBoundItem as IEditableObject;
if (editbaleObject != null)
{
     editbaleObject.EndEdit();
}

Use attached to reproduce.
- Check then try to uncheck the rows.

Workaround:
private void RadGridView1_CreateCell(object sender, GridViewCreateCellEventArgs e)
{
    if (e.CellType == typeof(GridCheckBoxHeaderCellElement))
    {
        e.CellElement = new MyHeaderCheckboxCellElement(e.Column, e.Row);
    }
}

class MyHeaderCheckboxCellElement : GridCheckBoxHeaderCellElement
{
    public MyHeaderCheckboxCellElement(GridViewColumn col, GridRowElement row) : base (col, row)
    { }
    protected override void checkbox_ToggleStateChanged(object sender, StateChangedEventArgs args)
    {
        base.checkbox_ToggleStateChanged(sender, args);
        var prop = this.ViewInfo.GetType().GetProperty("Version", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        int value = (int)prop.GetValue(this.ViewInfo);
        prop.SetValue(this.ViewInfo, --value);

    }
}

Use attached to reproduce.
- Open the data filter dialog from the excel-like filtering on the date column.
- The date time format in the editor is not respected.
- Consider the default cell editor as well.  

Workaround:

private void RadGridView1_CreateCompositeFilterDialog(object sender, GridViewCreateCompositeFilterDialogEventArgs e)
{
    var dialog = e.Dialog as CompositeDataFilterForm;
    dialog.DataFilter.EditorInitialized -= DataFilter_EditorInitialized;
    dialog.DataFilter.EditorInitialized += DataFilter_EditorInitialized;
 
    dialog.DataFilter.NodeFormatting -= DataFilter_NodeFormatting;
    dialog.DataFilter.NodeFormatting += DataFilter_NodeFormatting;
}
 
private void DataFilter_NodeFormatting(object sender, TreeNodeFormattingEventArgs e)
{
    var criteriaNode = e.NodeElement as DataFilterCriteriaElement;
    if (criteriaNode != null)
    {
        var node = criteriaNode.Data as DataFilterCriteriaNode;
        if (node.DescriptorValue != null && node.PropertyName == "Date")
        {
            criteriaNode.ValueElement.Text = ((DateTime?)node.DescriptorValue).Value.ToString("MM/dd/yyyy");
        }
    }
}
 
private void DataFilter_EditorInitialized(object sender, TreeNodeEditorInitializedEventArgs e)
{
    var editor = e.Editor as TreeViewDateTimeEditor;
    if (editor != null)
    {
        var element = editor.EditorElement as BaseDateTimeEditorElement;
        element.Format = DateTimePickerFormat.Custom;
        element.CustomFormat = "dd/MM/yyyy";
    }
}
 

To reproduce: setup self-reference hierarchy. Add a GridViewHyperlinkColumn and show the expander item in this column. Please refer to the attached screenshot. The hyperlink text overlaps with the expander.

Workaround: set the MasterTemplate.SelfReferenceExpanderColumn to a different column.