gong wpf dragdrop do not work

See more:

C#

C#4.0

I have some problem with gong-wpf-dragdrop. it does not work when I am drag from left to right.(But work from right to left) It's very strange. Why it's happening? Thanks!

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
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;
using System.Collections.ObjectModel;

namespace WpfApplication4
{
    public class DataStruct
    {
        public int number { get; set; }
        public string Name { get; set; }
    }
    [Serializable]
    public class TestSer
    {
        public ObservableCollection<DataStruct> Items { get; set; }
        public string Names { get; set; }
        public TestSer()
        {
            Items = new ObservableCollection<DataStruct>();
            Items.Add(new DataStruct { number = 1, Name = "First" });
            Items.Add(new DataStruct { number = 2, Name = "Two" });
            Items.Add(new DataStruct { number = 3, Name = "Three" });
        }
    }
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            this.DataContext = new TestSer();
            InitializeComponent();
        }
    }
}

<Window x:Class="WpfApplication4.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:dd="clr-namespace:GongSolutions.Wpf.DragDrop;assembly=GongSolutions.Wpf.DragDrop"
        Title="MainWindow" Height="350" Width="525">
    <ItemsControl dd:DragDrop.IsDragSource="True" dd:DragDrop.IsDropTarget="True" ItemsSource="{Binding Items}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <UniformGrid Rows="2" Columns="4" />
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Border BorderBrush="#FF000000" BorderThickness="1,1,1,1" CornerRadius="8,8,8,8" Margin="5">
                    <Grid>
                        <Grid.RowDefinitions>
                            <RowDefinition></RowDefinition>
                            <RowDefinition></RowDefinition>
                            <RowDefinition></RowDefinition>
                            <RowDefinition></RowDefinition>
                            <RowDefinition></RowDefinition>
                            <RowDefinition></RowDefinition>
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition></ColumnDefinition>
                            <ColumnDefinition></ColumnDefinition>
                        </Grid.ColumnDefinitions>
                        <Label Grid.Row="0" Content="{Binding Name}" ></Label>
                        <Label Grid.Row="1" Content="{Binding number}"></Label>
                    </Grid>
                </Border>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</Window>