Working with PasteOptionsPopup may cause an exception in LayoutElement.SetParent. Very difficult to reproduce, having no consistent steps. Maybe it is related to undo of paste command, but there are no other clues aside from this.

In this feature, the existing text is overridden as the user types on it with the "Insert" key is pressed on the keyboard.

Workaround: Track the state of the Insert key and delete before inserting content using the KeyDown and CommandExecuting events:

private void MainDemoControl_KeyDown(object sender, System.Windows.Input.KeyEventArgs e)
{
    if (e.KeyboardDevice.IsKeyToggled(Key.Insert))
    {
        this.isInsertKeyPressed = true;
    }
    else
    {
        this.isInsertKeyPressed = false;    
    }
}
private void radRichTextBox_CommandExecuting(object sender, CommandExecutingEventArgs e)
{
    if (e.Command is InsertTextCommand && this.isInsertKeyPressed)
    {
        this.radRichTextBox.Delete(false);
    }
}

Using the microsoft word,In docx document,inserting a shape,and add the text context to the shape,then save.

when radrichtextbox  open the file,the program crashed.

When a whole paragraph is selected and the Set Numbering Value command is executed, the numbering value of the next paragraph is changed instead of the current one.

private void radRichTextBox_CommandExecuting(object sender, CommandExecutingEventArgs e)
{
    if (e.Command is ShowSetNumberingValueDialogCommand)
    {
        this.radRichTextBox.Document.CaretPosition.MoveToPosition(this.radRichTextBox.Document.Selection.Ranges.First.StartPosition);
    }
}

The issue is observed when the added table is preceded by a paragraph with a font size different from the default one. As the issue is caused by a broken mouse capture, the following workaround can be employed:

someRandomFrameworkElement.CaptureMouse();

someRandomFrameworkElement.ReleaseMouseCapture();