Why Text colour not changed on drag and drop froma ListBox to another ListBox using IvalueConverter ?

I have two ListBoxes and each of them have a TextBlock inside (from a DataTemplate). I have two buttons to transfer the text from one list box to the other, and vice versa.

I also allow the user to drag and drop to move text from one ListBox to another, which functionally works fine.

However for my buttons, I use "Style="{Binding IsInGroup, Converter={StaticResource StyleFunctionConverter}}" and when the selected button appears on the other list on button click then it changes the text style and color, but when I try to transfer the text using drag and drop it just simply transfers the text and does not change text color.

My code:

<UserControl.Resources><local:StyleFunctionConverter x:Key="StyleFunctionConverter" /></UserControl.Resources><Grid x:Name="LayoutRoot" Background="{StaticResource BGBrush_1}"><Grid.ColumnDefinitions><ColumnDefinition Width="Auto" /><ColumnDefinition/></Grid.ColumnDefinitions><Grid Width="200"><Grid.RowDefinitions><RowDefinition/><RowDefinition Height="Auto" /></Grid.RowDefinitions>
        //First ListBox each ListBox inside scrollviewer<ScrollViewer Grid.Column="1" ScrollViewer.HorizontalScrollBarVisibility="Auto" ScrollViewer.VerticalScrollBarVisibility="Auto" Style="{StaticResource MP_ScrollViewerStyle}" BorderBrush="{x:Null}"><Grid Margin="40,20"><Grid.RowDefinitions><RowDefinition Height="Auto" /><RowDefinition Height="Auto" /><RowDefinition Height="Auto" /></Grid.RowDefinitions><ScrollViewer Grid.Row="1" Margin="5,5,5,5" HorizontalAlignment="Center" ScrollViewer.HorizontalScrollBarVisibility="Auto" ScrollViewer.VerticalScrollBarVisibility="Auto" Style="{StaticResource MP_ScrollViewerStyle}" BorderBrush="{x:Null}"><toolKit:ListBoxDragDropTarget AllowDrop="True" Grid.Row="1" Grid.Column="1"><ListBox x:Name="GroupFunctionListBox" Width="200" Height="Auto" SelectionMode="Extended" ItemsSource="{Binding GroupFunctionList}" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Foreground="White" Background="{StaticResource BGBrush_1}"><ListBox.ItemTemplate><DataTemplate><TextBlock Text="{Binding Label}" Style="{Binding IsInGroup, Converter={StaticResource StyleFunctionConverter}}" /></DataTemplate></ListBox.ItemTemplate></ListBox></toolKit:ListBoxDragDropTarget></ScrollViewer>
                //These are the two buttons (=> and<=, the content is &lg and &gt) <Button Content="&lt;=" x:Name="AddButton" Grid.Row="1" Grid.Column="1" Height="23" HorizontalAlignment="Left" Margin="10,0,10,40" VerticalAlignment="Center" Width="75" Click="AddButton_Click" Style="{StaticResource ButtonStyle_Blue}" /><Button Content="=&gt;" x:Name="RemoveButton" Grid.Row="1" Grid.Column="1" Height="23" HorizontalAlignment="Left" Margin="10,80,10,0" VerticalAlignment="Center" Width="75" Click="RemoveButton_Click" Style="{StaticResource ButtonStyle_Blue}" /><ScrollViewer Grid.Row="1" Grid.Column="2" Margin="5,5,5,5" HorizontalAlignment="Center" ScrollViewer.HorizontalScrollBarVisibility="Auto" ScrollViewer.VerticalScrollBarVisibility="Auto" Style="{StaticResource MP_ScrollViewerStyle}" BorderBrush="{x:Null}"><toolKit:ListBoxDragDropTarget AllowDrop="True" Grid.Row="1" Grid.Column="2"><ListBox x:Name="OtherFunctionListBox" Width="200" HorizontalAlignment="Center" ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Disabled" Height="Auto" SelectionMode="Extended" ItemsSource="{Binding OtherFunctionList}" Foreground="White" Background="{StaticResource BGBrush_1}"><ListBox.ItemTemplate><DataTemplate><TextBlock Text="{Binding Label}" Style="{Binding IsInGroup, Converter={StaticResource StyleFunctionConverter}}" /></DataTemplate></ListBox.ItemTemplate></ListBox></toolKit:ListBoxDragDropTarget></ScrollViewer></Grid>

My converter class is : (StyleFunctionConverter)

public class StyleFunctionConverter : IValueConverter
    {
        public Object Convert(Object value, Type targetType, Object parameter, CultureInfo culture)
        {
            if (value == null)
                return null;

            bool isInGroup = (bool)value;
            if (isInGroup)
                return Application.Current.Resources["ListBoxTextNormalItem"];
            else
                return Application.Current.Resources["ListBoxTextChangeItem"];
        }

        public Object ConvertBack(Object value, Type targetType, Object parameter, CultureInfo culture)
        {
            return null;
        }
    }

button click events are :

private void AddButton_Click(object sender, RoutedEventArgs e)
        {
            ((GroupViewModel)this.DataContext).AddFunctionGroup((ObservableCollection<object>)OtherFunctionListBox.SelectedItems);
        }

View Model class is:

    public ObservableCollection<Function> GroupFunctionList
            {
                get
                {
                    return groupFunctionList;
                }
                set
                {
                    groupFunctionList = value;
                    NotifyPropertyChanged("GroupFunctionList");
                }
            }
            private ObservableCollection<Function> otherFunctionList;
            /// <summary>
            /// groupList
            /// </summary>
            public ObservableCollection<Function> OtherFunctionList
            {
                get
                {
                    return otherFunctionList;
                }
                set
                {
                    otherFunctionList = value;
                    NotifyPropertyChanged("OtherFunctionList");
                }
            }
        public class StyleFunctionConverter : IValueConverter
            {
                public Object Convert(Object value, Type targetType, Object parameter, CultureInfo culture)
                {
                    if (value == null)
                        return null;
                    bool isInGroup = (bool)value;
                    if (isInGroup)
                        return Application.Current.Resources["ListBoxTextNormalItem"];
                    else
                        return Application.Current.Resources["ListBoxTextChangeItem"];
                }
                public Object ConvertBack(Object value, Type targetType, Object parameter, CultureInfo culture)
                {
                    return null;
                }
            }
    button click events are :
         private void AddButton_Click(object sender, RoutedEventArgs e)
                {
                    ((GroupViewModel)this.DataContext).AddFunctionGroup((ObservableCollection<object>)OtherFunctionListBox.SelectedItems);
                }
    And ViewModel Class is:
           public void AddFunctionGroup(ObservableCollection<object> selectedOtherFunction)
            {
                if (selectedOtherFunction != null)
                {
                    List<Function> funcList = new List<Function>();
                    foreach (object func in selectedOtherFunction)
                        funcList.Add((Function)func);
                    foreach (Function func in funcList.OrderBy(c => c.Label))
                    {
                        if (SelectedGroup != null && !SelectedGroup.GroupFunctionList.Contains(func))
                            func.IsInGroup = false;
                        else
                            func.IsInGroup = true;
                        GroupFunctionList.Add(func);
                        OtherFunctionList.Remove(func);
                    }   
                    reorderGroup();
                }
            }
            public void reorderGroup()
            {
                List<Function> TMPGroupFunctionList = new List<Function>();
                foreach (Function gfl in GroupFunctionList.OrderBy(c => c.Label))
                {
                    TMPGroupFunctionList.Add(gfl);
                }
                GroupFunctionList.Clear();
                foreach (Function gfl in TMPGroupFunctionList.OrderBy(c => c.Label))
                {
                    GroupFunctionList.Add(gfl);
                }
                List<Function> TMPOtherFunctionList = new List<Function>();
                foreach (Function ofl in OtherFunctionList.OrderBy(c => c.Label))
                {
                    TMPOtherFunctionList.Add(ofl);
                }
                OtherFunctionList.Clear();
                foreach (Function ofl in TMPOtherFunctionList.OrderBy(c => c.Label))
                {
                    OtherFunctionList.Add(ofl);
                }
            }