How to enable user interface virtualization in a standard WPF ListView

I am using .NET 4.5 / VS2012 and my ListView looks something like this.

<ListView 
    VirtualizingPanel.IsContainerVirtualizable="True"
    VirtualizingPanel.IsVirtualizing="True"
    VirtualizingPanel.IsVirtualizingWhenGrouping="True"
    Grid.Row="1"
    Name="eventLogList"
    Margin="5,0,5,0"
    BorderBrush="Black"
    BorderThickness="2"
    ItemsSource="{Binding EventLogs}"
    SelectedItem="{Binding SelectedEventLog}"
    local:ListViewSorter.CustomListViewSorter="EventLogViewer.UI.EventLogItemComparer"
    SelectionMode="Single">

    <ListView.GroupStyle>
        <GroupStyle HidesIfEmpty="False">
            <GroupStyle.ContainerStyle>
                <Style TargetType="GroupItem">
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="GroupItem">
                                <Expander IsExpanded="True">
                                    <Expander.Header>
                                        <TextBlock FontSize="20" TextWrapping="Wrap" Margin="0,10,0,5" >
                                        <Bold><TextBlock Text="{Binding Name}"/></Bold> - <TextBlock FontSize="20" Text="{Binding ItemCount}"/> logs
                                    </TextBlock>
                                    </Expander.Header>
                                    <ItemsPresenter/>
                                </Expander>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </GroupStyle.ContainerStyle>
        </GroupStyle>
    </ListView.GroupStyle>
    <ListView.View>
        <GridView>
            <GridViewColumn 
                Header="event id"
                Width="120"
                DisplayMemberBinding="{Binding EventID}" />
            <GridViewColumn 
                Header="level"
                Width="160"
                DisplayMemberBinding="{Binding Level}" />
            <GridViewColumn 
                Header="server" 
                Width="160"
                DisplayMemberBinding="{Binding Server}" />
            <GridViewColumn 
                Header="log name" 
                Width="160"
                DisplayMemberBinding="{Binding LogName}" />
            <GridViewColumn 
                Header="source"
                Width="240"
                DisplayMemberBinding="{Binding Source}" />
            <GridViewColumn 
                Header="logged"
                Width="240"
                DisplayMemberBinding="{Binding Logged}" />
        </GridView>
    </ListView.View>
</ListView>

But still, performance is not improving at all. I found an example using ListBox, but how to virtualize ListView? I did a little work. I heard that with grouping, virtualization is disabled in a previous version of WPF, but with .NET 4.5 WPF has a property IsVirtualizingWhenGrouping, I already set it to True.

Update : the culprit is the usual style, after removing it, the list view runs smoothly, like butter