Selected row of RadGridView does not display text!!

My company security policy block uploading image.

So, I will post a sample source (.cs and .xaml).

While this program is running, click and select some row.

Then selected row shows just all blue bar without text.... 

First. xaml code--------------------------------------------

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation" x:Class="WpfApplication2.MainWindow"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="System.Windows.xaml" />
                <ResourceDictionary Source="Telerik.Windows.Controls.xaml" />
                <ResourceDictionary Source="Telerik.Windows.Controls.Input.xaml" />
                <ResourceDictionary Source="Telerik.Windows.Controls.GridView.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Window.Resources>
    <Grid>

        <telerik:RadGridView 
            x:Name="data"
          AutoGenerateColumns="False" 
        CanUserFreezeColumns="False" 
        CanUserResizeColumns="True"
        ShowGroupPanel="False"
        RowIndicatorVisibility="Collapsed"                 
        AutoExpandGroups="True"        
                IsReadOnly="False"
                HorizontalAlignment="Stretch" Height="Auto"  VerticalAlignment="Stretch" Width="Auto">
            <telerik:RadGridView.Columns>
                <telerik:GridViewDataColumn Header="A" Width="50" DataMemberBinding="{Binding A, Mode=TwoWay}"/>
                <telerik:GridViewDataColumn Header="C" Width="50" DataMemberBinding="{Binding B, Mode=TwoWay}"/>
                <telerik:GridViewDataColumn Header="D" Width="50" DataMemberBinding="{Binding C, Mode=TwoWay}"/>
                <telerik:GridViewDataColumn Header="E" Width="50" DataMemberBinding="{Binding D, Mode=TwoWay}"/>
            </telerik:RadGridView.Columns>
        </telerik:RadGridView>

    </Grid>
</Window>

And .cs Code ---------------------------------------------------------------------------------

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApplication2
{
    public class tdata
    {
        public string A{get; set;}
        public string B{get; set;}
        public string C{get; set;}
        public string D{get; set;}
    }
    /// <summary>
    /// MainWindow.xaml에 대한 상호 작용 논리
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            data.Items.Add(new tdata() { A = "11", B = "22", C = "33", D = "44" });
            data.Items.Add(new tdata() { A = "11", B = "22", C = "33", D = "44" });
            data.Items.Add(new tdata() { A = "11", B = "22", C = "33", D = "44" });
            data.Items.Refresh();
        }
    }
}