Wierd issue with button click event

Dear all,

I have a strange beaviour with a button click event.

I have a main windows which display a map( it could be anything else). The main windows is based on a main grid where controls gets align in. I have define in my case as a part of that main window a set of control that act like a bottom menu bar ( imagine a bottom menu bar on Windows 8 when you slide your finger from down to up) that I render visible when the user touch is finger at the range of 50 pixel from the bottom area. When hit the bottom bar appears with a set of button control.

In order to perform the visibility of the bottom menu bar I need to handle the PreviewMouseDown in order to identify touch position. that event is applied on my main grid and defined as follow :

private void _LayoutRoot_PreviewMouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
                          AppState.Instance.FingerPosition = e.Device.GetPosition(this);

                //check area of touch in order to show sysem commands
                if ((this.ActualWidth - AppState.Instance.FingerPosition.X) <= 50) ViewModelLocator.WorldMapViewModelStatic.ShowSystemCommandRight = true;
                else ViewModelLocator.WorldMapViewModelStatic.ShowSystemCommandRight = false;

                if (AppState.Instance.FingerPosition.X <= 50)  ViewModelLocator.WorldMapViewModelStatic.ShowSystemCommandLeft = true;
                else ViewModelLocator.WorldMapViewModelStatic.ShowSystemCommandLeft = false;

                //check area of touch in order to show bottom and top commands
                if ((this.ActualHeight - AppState.Instance.FingerPosition.Y) <= 50 || AppState.Instance.FingerPosition.Y <= 50)
                    ViewModelLocator.WorldMapViewModelStatic.ShowCommands = !ViewModelLocator.WorldMapViewModelStatic.ShowCommands && !ViewModelLocator.MainViewModelStatic.UserNotification.IsVisible;
                else ViewModelLocator.WorldMapViewModelStatic.ShowCommands = false;

                   }

The button layout in the grid are defined as follow:

<Border Style="{StaticResource DynamicCommandBorder}" Grid.ColumnSpan="3" Grid.Row="2" Height="70" Background="Black" Visibility="{Binding Source={StaticResource Locator},Path=MainViewModel.IsSurfaceMode,UpdateSourceTrigger=PropertyChanged,Converter={StaticResource BoolNotVisibilityConverter}}"><Grid><StackPanel x:Name="BottomCommand" Grid.ColumnSpan="3" Grid.Row="2" Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center"
                    Visibility="{Binding Source={StaticResource Locator},Path=MainViewModel.AppInInactivityMode,UpdateSourceTrigger=PropertyChanged,Converter={StaticResource BoolNotVisibilityConverter}}"><controls:MapButtonControl Margin="0,0,0,0" Tag="{Binding ElementName=BottomCommand,Path=Name}" DataContext="{Binding Source={StaticResource Locator}, Path=MapButtonsViewModel.MapModeButtons[0]}"/><controls:MapButtonControl Margin="20,0,0,0" Tag="{Binding ElementName=BottomCommand,Path=Name}" DataContext="{Binding Source={StaticResource Locator}, Path=MapButtonsViewModel.MapModeButtons[1]}"/><controls:MapButtonControl Margin="20,0,0,0" Tag="{Binding ElementName=BottomCommand,Path=Name}" DataContext="{Binding Source={StaticResource Locator}, Path=MapButtonsViewModel.MapModeButtons[2]}"/><Grid Margin="40,0,0,0"><Grid.RowDefinitions><RowDefinition Height="Auto"/><RowDefinition Height="Auto"/></Grid.RowDefinitions><Button x:Name="_buRotate2" Click="_buRotate2_Click"  Background="Black" ><Image RenderOptions.BitmapScalingMode="HighQuality" Width="25" Height="25" HorizontalAlignment="Center" Source="../Resources/Pictos/mapRotate.png"/></Button><TextBlock Grid.Row="1" Text="{Binding Source={x:Static props:Resources.Bu_MapRotateMode_Title}}" FontSize="10"  
                                   TextAlignment="Center" VerticalAlignment="Bottom" HorizontalAlignment="Center" 
                                   TextWrapping="Wrap"  
                                   Foreground="White" /></Grid></StackPanel><StackPanel x:Name="BottomsysCommand" Grid.ColumnSpan="3" Grid.Row="2" Orientation="Horizontal" HorizontalAlignment="Left" VerticalAlignment="Center"
                    Visibility="{Binding Source={StaticResource Locator},Path=MainViewModel.AppInInactivityMode,UpdateSourceTrigger=PropertyChanged,Converter={StaticResource BoolNotVisibilityConverter}}"><controls:MapModeCommandContentControl Margin="40,0,0,0"/></StackPanel></Grid></Border>

The weird behavior I met here is that when I try to click on any button, none of the button events gets raised. If I remove the PreviewMouseDown event, all works fine.

What did I miss here ?

Thnaks for your help

regards