LstBox Selected Item with Checkbox Problem - WPF

<Controls:MetroWindow x:Class="Outlook_Add_In_Test.WPFDistroList"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d"
             xmlns:Controls="clr-namespace:MahApps.Metro.Controls;assembly=MahApps.Metro"
             d:DesignHeight="410" MaxHeight="410" Title="Distribution List" MaxWidth="340" ResizeMode="NoResize" WindowStartupLocation="CenterScreen" Width="257">

    <Controls:MetroWindow.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Colours.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
                <ResourceDictionary Source="Theme/DeFacto.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/BaseLight.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.AnimatedTabControl.xaml" />
                <ResourceDictionary Source="Theme/FlatButton.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Controls:MetroWindow.Resources>

    <Grid>

        <ListBox x:Name="LstDistro" ItemsSource="{Binding}" HorizontalAlignment="Left" Margin="10,10,0,42" Width="235" BorderBrush="Black" BorderThickness="2,2,1,1" SelectionMode="Multiple" SelectionChanged="LstDistro_SelectionChanged">

            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <Canvas x:Name="EventItem" HorizontalAlignment="Left" Height="42" VerticalAlignment="Top" Width="215" Background="{Binding Path=LBackground}">
                            <Label Content="{Binding LInits}" HorizontalAlignment="Left" Height="33" VerticalAlignment="Top" Width="40" FontWeight="Bold" FontSize="12" Canvas.Top="5"/>
                            <Label Content="{Binding LFullName}" HorizontalAlignment="Left" Height="33" VerticalAlignment="Top" Width="164" FontSize="12" Canvas.Left="40" Canvas.Top="5"/>
                            <CheckBox x:Name="ChkName" IsChecked="{Binding IsSelected}" Height="20" Width="20" Canvas.Left="190" Canvas.Top="12" Checked="CheckBox_Checked" />
                        </Canvas>
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>

            <ListBox.ItemContainerStyle>
                <Style TargetType="ListBoxItem">
                    <Setter Property="IsSelected" Value="{Binding IsSelected}"/>
                </Style>
            </ListBox.ItemContainerStyle>

        </ListBox>

        <Controls:ProgressRing x:Name="LoadingRing" IsActive="False" Margin="95,142,96,0" VerticalAlignment="Top"/>
        <Button x:Name="BtnOk" Content="Ok" HorizontalAlignment="Left" Height="36" Margin="68,340,0,0" VerticalAlignment="Top" Width="123" Background="#FF333333" Foreground="White" FontFamily="Arial" FontWeight="Normal" FontSize="14" Click="BtnOk_Click"/>
    </Grid>
</Controls:MetroWindow>