WPF Button doesn't execute Command

I have a ListViewItem which has an Eventhandler attatched and inside the ControlTemplate of the ListViewItem is a Button which does something different. But if I click the Button, the Behaviour is like I clicked on the ListViewItem.

AppointmentOverview.xaml:

<Window.Resources>        
    <Style TargetType="{x:Type ListViewItem}" BasedOn="{StaticResource NormalListViewItem}">
        <EventSetter Event="PreviewMouseLeftButtonDown" 
            Handler="ListViewItem_PreviewMouseLeftButtonDown" />
    </Style>
</Window.Resources>

Styles.xaml(My ResourceDictionary):

<!--Style für die normalen ListViewItems-->
<Style x:Key="NormalListViewItem" TargetType="{x:Type ListViewItem}">       
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ListViewItem}">
                <Border BorderBrush="#5076A7" BorderThickness="1">
                    <Border.Background>
                        <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
                            <GradientStop Color="#FFFFFF" Offset="0.0"/>
                            <GradientStop Color="#FFFEB603" Offset="1.0"/>
                        </LinearGradientBrush>
                    </Border.Background>
                    <StackPanel TextElement.FontFamily="Segoe UI" TextElement.FontSize="12">
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="*"/>
                                <ColumnDefinition Width="15"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="*"/>
                            </Grid.RowDefinitions>
                            <TextBlock Name="Betreff" Padding="3,0,0,0" Text="{Binding Betreff}" TextTrimming="CharacterEllipsis" Grid.Column="0" Grid.Row="0"/>
                            <Button Grid.Column="1" Grid.Row="0" Style="{StaticResource ListViewItemButton}"/>

AppointmentOverview.xaml.cs:

private void ListViewItem_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    var item = sender as ListViewItem;
    if (item != null)
    {
        AppointmentOverviewViewModel apvm = this.DataContext as AppointmentOverviewViewModel;
        apvm.editAppointment(item);
    }
}

It worked when I had the complete ListViewItem Style in the Window.Resources of Appointmentoverview.xaml. But I didn't like that because the would kind of beat the purpose of Styles.xaml. Also I didn't have a Style for the Button, just did all the Styling inside the Button. But this was very Basic and now I need more complex Styling so I wanted to create a separate Style.

<Button FontSize="7" Content="X" Grid.Column="1" Grid.Row="0" 
    Command="{Binding DataContext.DeleteButtonCommand, RelativeSource={
    RelativeSource AncestorType={x:Type Window}}}" CommandParameter="{Binding ItemId}"/>  

Update:
If I observe my EventHandler this is also triggered if the Button is pressed. It just says the source is a Button but the command is not executed.

Styles.xaml.cs

void ListViewItem_MouseLeftDown(object sender, MouseButtonEventArgs e)
    {
        DependencyObject current = sender as DependencyObject;
        while (current != null && current.GetType() != typeof(ListViewItem))
        {
            current = VisualTreeHelper.GetParent(current);
        }
        var item = current as ListViewItem;
        if (item != null)
        {
            Window parent = Window.GetWindow(current);
            AppointmentOverviewViewModel apovm = parent.DataContext as AppointmentOverviewViewModel;
            apovm.editAppointment(item);
        }

    }

Styles.xaml

<!--DataTemplate für die normalen ListViewItems-->
<DataTemplate DataType="{x:Type local:SCSMAppointment}">
    <Border BorderBrush="#5076A7" BorderThickness="1" PreviewMouseLeftButtonDown="ListViewItem_MouseLeftDown">
        <Border.Background>
            <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
                <GradientStop Color="#FFFFFF" Offset="0.0"/>
                <GradientStop Color="#FFFEB603" Offset="1.0"/>
            </LinearGradientBrush>
        </Border.Background>
        <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition Height="*"/>
                    <RowDefinition Height="*"/>
                    <RowDefinition Height="*"/>
                </Grid.RowDefinitions>
            <DockPanel Grid.Row="0">
                <Button FontSize="7" Content="X" DockPanel.Dock="Right" Width="15"
                                        Command="{Binding DataContext.DeleteButtonCommand, RelativeSource={RelativeSource AncestorType={x:Type Window}}}" 
                                        CommandParameter="{Binding ItemId}"/>
                <TextBlock Name="Betreff" Padding="3,0,0,0" Text="{Binding Betreff}" TextTrimming="CharacterEllipsis" />

            </DockPanel>
            <StackPanel Orientation="Horizontal" Grid.Row="1">
                <TextBlock Padding="3,0,0,0" Text="{Binding Kunde}"/>
                <TextBlock Padding="3,0,0,0" Text="|"/>
                <TextBlock Padding="3,0,0,0" Text="{Binding IncidentId}"/>
            </StackPanel>
            <StackPanel Orientation="Horizontal" Grid.Row="2">
                <TextBlock FontWeight="Bold" Padding="3,0,0,0" Text="{Binding Ort}"/>
                <TextBlock Padding="3,0,0,0" Text="("/>
                <TextBlock Text="{Binding Alternative}"/>
                <TextBlock Text=")"/>
            </StackPanel>
        </Grid>
    </Border>        
</DataTemplate>