To reproduce:
- Filter a self-referencing grouped grid. 

Workaround:
private void _rgvFreeCodeValues_FilterChanged(object sender, GridViewCollectionChangedEventArgs e)
{
    foreach (var row in RgvFreeCodeValues.Rows)
        row.IsExpanded = false;
}

private void _rgvFreeCodeValues_FilterChanging(object sender, GridViewCollectionChangingEventArgs e)
{
    foreach (var row in RgvFreeCodeValues.Rows)
        row.IsExpanded = true;
}

How to reproduce: 
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        ThemeResolutionService.AllowAnimations = false;
        this.radGridView1.DataSource = this.GetData();
    }

    private DataTable GetData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Id", typeof(int));
        dt.Columns.Add("Name", typeof(string));
        dt.Rows.Add(1, "\u0002x09");
        for (int i = 1; i < 10; i++)
        {
            dt.Rows.Add(i, "name");
        }

        return dt;
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        GridViewSpreadExport spreadExporter = new GridViewSpreadExport(this.radGridView1);
        spreadExporter.FileExportMode = FileExportMode.CreateOrOverrideFile;
        SpreadExportRenderer exportRenderer = new SpreadExportRenderer();
        spreadExporter.RunExport(@"..\..\exported-file.xlsx", exportRenderer);
    }
}

ArgumentException with clarification similar to  "'\u001f', hexadecimal value 0x1F, is an invalid character." is thrown when trying to export document containing characters which are not supported in XML document - such as some control characters like 0x00, 0x1F, 0x1B, etc. Such characters are described in the XML specification here: https://www.w3.org/TR/xml/#charsets.

Although the escaped strings are not supported (see  https://feedback.telerik.com/Project/184/Feedback/Details/190228 ), the library could prevent the exception and export the document successfully by skipping such characters.

Workaround: remove such characters before the export. Check the following StackOverflow answer for some ideas on code for replacing the characters: http://stackoverflow.com/a/14323524/259206

A similar issue can be also observed in RadTreeView:

Workaround RadGridView: 
private void RadGridView1_CellEditorInitialized(object sender, GridViewCellEventArgs e)
{
    RadTextBoxEditor editor = e.ActiveEditor as RadTextBoxEditor;
    if (editor != null)
    {
        editor.EditorElement.MinSize = new Size(0, 30);
    }
}

Workaround RadTreeView:
 
private void RadTreeView1_EditorInitialized(object sender, TreeNodeEditorInitializedEventArgs e)
{
    TreeViewTextBoxEditor editor = e.Editor as TreeViewTextBoxEditor;
    if (editor != null)
    {
        ((BaseTextBoxEditorElement)editor.EditorElement).TextBoxItem.TextBoxControl.MinimumSize = new Size(0, 24);
    }
}

In 125% the RadTextBox in the Fluent theme keeps shrinking:

Workaround
public RadForm1()
{
    InitializeComponent();

    SizeF dpi = NativeMethods.GetMonitorDpi(Screen.PrimaryScreen, NativeMethods.DpiType.Effective);
    this.radTextBox1.MinimumSize = new Size(0, (int)(24 * dpi.Height));
}

To reproduce: run the attached sample project. 

Type "chef" in the search box and then try to sort some of the columns. Click the header cell several times and as a result the exception will occur.

Workaround:

        public class CustomGrid : RadGridView
        {
            public new object DataSource
            { 
                get
                {
                    return (object)base.DataSource;
                }
                set
                {
                    GridViewSearchRowInfo.Cancel = true;
                    Thread.Sleep(100);
                    base.DataSource = null;
                    this.EnableFiltering = false;
                    base.DataSource = value;
                    this.EnableFiltering = true;
                    base.CurrentRow = null; 
                }
            }
        }

To reproduce:

Please run the sample project and follow the steps from the gif file.

Workaround:

        private void radGridView1_SizeChanged(object sender, EventArgs e)
        {
            this.radGridView1.MasterTemplate.Refresh();
        }

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

            protected override void OnResize(EventArgs e)
            {
                object value = null;
                if (this.ActiveEditor != null)
                { 
                    value = this.ActiveEditor.Value;  
                }
                base.OnResize(e);
                if (value != null && this.CurrentCell != null)
                {
                    this.CurrentCell.Value = value;
                }
            }
        }

How to reproduce: Create a DPI-aware application and run it on a Windows 10 machine on 125%, the text inside the editors is smaller compared to the text in cells which are not in edit mode.

Workaround: 
private void RadGridView1_CellEditorInitialized(object sender, GridViewCellEventArgs e)
{
    BaseInputEditor editor = e.ActiveEditor as BaseInputEditor;

    if (editor != null)
    {
        RadTextBoxItem item = editor.EditorElement.FindDescendant<RadTextBoxItem>();

        if (item != null)
        {
            item.HostedControl.Font = this.radGridView1.GridViewElement.GetScaledFont(this.radGridView1.GridViewElement.DpiScaleFactor.Height);
        }
    }
} 

To reproduce:
Use the following code
private void RadGridView1_UserAddingRow(object sender, GridViewRowCancelEventArgs e)
{
    radGridView1.MasterView.TableAddNewRow.CancelAddNewRow();
    radGridView1.MasterView.ViewTemplate.DataView.CurrentItem.IsCurrent = false;
}

Place the new row at the bottom. While in edit mode press tab to fill until an exception is thrown.

Workaround:
BaseGridBehavior gridBehavior = radGridView1.GridBehavior as BaseGridBehavior;
gridBehavior.UnregisterBehavior(typeof(GridViewNewRowInfo));
gridBehavior.RegisterBehavior(typeof(GridViewNewRowInfo), new CustomGridRowBehavior());


internal class CustomGridRowBehavior : GridNewRowBehavior
{
    protected override bool ProcessTabKey(KeyEventArgs keys)
    {
        bool newRowIsInEditMode = this.IsInEditMode && this.GridViewElement.CurrentRow is GridViewNewRowInfo;

        if ( newRowIsInEditMode  && this.GridViewElement.Navigator.IsLastEditableColumn(this.GridViewElement.CurrentColumn))              
        {
            this.GridViewElement.Navigator.SelectFirstColumn();

            while (this.GridViewElement.CurrentColumn.ReadOnly && this.GridViewElement.Navigator.SelectNextColumn())
            { }
            return false;
        }
        return base.ProcessTabKey(keys);
    }
}

To reproduce:
private void RadGridView1_UserAddingRow(object sender, Telerik.WinControls.UI.GridViewRowCancelEventArgs e)
{
    radGridView1.MasterView.TableAddNewRow.CancelAddNewRow();
}
See attached video.

Workaround:
private void RadGridView1_UserAddingRow(object sender, Telerik.WinControls.UI.GridViewRowCancelEventArgs e)
{
    radGridView1.MasterView.TableAddNewRow.CancelAddNewRow();
    radGridView1.MasterView.ViewTemplate.DataView.CurrentItem.IsCurrent = false;
}

Use attached to reproduce.

With versions prior 2015.3.930 the results are different.

To reproduce:  run the attached sample project and click the 'export' button. The exported file fill be automatically opened. If you select several cells from the UnitPrice column you will see at the bottom that the cell values ' total is displayed. However, if you include  the summary item's value in the selection its value is not taken into consideration.  If you pay attention to the cell's format, it will be General instead of custom numeric one.

Workaround: 

    Private Sub spreadExporter_CellFormatting(sender As Object, e As Telerik.WinControls.Export.CellFormattingEventArgs)
        If e.GridRowInfoType = GetType(GridViewSummaryRowInfo) AndAlso e.GridCellInfo.ColumnInfo.Name = "DecimalColumn" Then
            Dim cellSelection As CellSelection = TryCast(e.CellSelection, CellSelection)
            Dim cellFormat As New CellValueFormat("### ### ###.00")
            If cellFormat IsNot Nothing Then
                cellSelection.SetValue(Decimal.Parse(cellSelection.GetValue().Value.RawValue.Replace(" ", "")))
                cellSelection.SetFormat(cellFormat)
            End If 
        End If 
    End Sub

To reproduce:
private void radButton1_Click(object sender, EventArgs e)
{
    radGridView1.MasterView.TableSearchRow.SelectNextSearchResult();

}
Check the index in the search textbox, it is not updated. 

Workaround:
var cell = radGridView1.TableElement.FindDescendant<GridSearchCellElement>();
if (cell != null)
{
    cell.FindNextButton.PerformClick();
}

To reproduce: 
            DataTable dt = new DataTable();
            dt.Columns.Add("Id", typeof(int));
            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("NumberAsShort", typeof(ushort));
            for (int i = 0; i < 100; i++)
            {
                dt.Rows.Add(i, "Row" + i, i );
            }
            this.radGridView1.DataSource = dt;

Workaround: use the CellFormatting event https://docs.telerik.com/devtools/winforms/gridview/cells/formatting-cells

To reproduce, perform the following steps with the attached project:

Step 1: Create Sample Database
==============================
New (Sample1.db)
Import
Save
Close

Step 2:
======
Open (Sample1.db)
Import
Save
Close

Step 3:
======
New (Sample2.db)
Import (Exception)

Workaround:
 radGridView1.GridViewElement.Navigator = new MyNavigator();

class MyNavigator : BaseGridNavigator
{
    public override bool SelectLastRow()
    {
        var enumerator = typeof(BaseGridNavigator).GetField("enumerator", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(this) as GridTraverser;
        enumerator.Reset();
      
        return base.SelectLastRow();
    }
}

Use attached to reproduce.

Workaround:

Use CellFormatting instead of RowFormating. 

Workaround: adjust the cell/row spacing

        this.radGridView1.TableElement.CellSpacing = -2;
        this.radGridView1.TableElement.RowSpacing = -2;

To reproduce: run the attached sample project and press the "stream export" button. 

Workaround: use the GridViewSpreadExport https://docs.telerik.com/devtools/winforms/gridview/exporting-data/spread-export

        Dim spreadExporter As GridViewSpreadExport = New GridViewSpreadExport(RadGridView1)
        Dim exportRenderer As New SpreadExportRenderer()
        Dim fileName As String = "..\..\Export" & DateTime.Now.ToLongTimeString().Replace(":", "_") + ".xlsx"
        spreadExporter.RunExport(fileName, exportRenderer)

Workaround: 

        private void radGridView1_CellFormatting(object sender, Telerik.WinControls.UI.CellFormattingEventArgs e)
        {
            GridDataCellElement cell = e.CellElement as GridDataCellElement ;
            if (cell!=null && cell.SelfReferenceLayout!=null)
            {

                foreach (RadElement item in cell.SelfReferenceLayout.StackLayoutElement.Children)
                {
                    if (!(item is GridTreeExpanderItem))
                    {
                        item.Visibility = ElementVisibility.Collapsed;
                    }
                    else
                    {
                        item.Visibility = ElementVisibility.Visible;
                    }
                } 
            } 
        }

Use attached to reproduce.

Workaround:

DragDropService.AllowAutoScrollColumnsWhileDragging = false;
DragDropService.AllowAutoScrollRowsWhileDragging = false;