Treelistbox IsExpanded xaml binding

Hi,

for some reason the binding of IsExpanded does nothing, visibility however works fine.

        <grids:TreeListBox
            Name="ProjectTreeListBox"
            Grid.Row="2"
            IsRootItemVisible="False"
            RootItem="{Binding Projects}">
            <grids:TreeListBox.ItemAdapter>
                <grids:TreeListBoxItemAdapter ChildrenBinding="{Binding Children}" TopLevelExpandabilityDefault="Auto" />
            </grids:TreeListBox.ItemAdapter>
            <grids:TreeListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Image
                            Width="16"
                            Height="16"
                            Stretch="None">
                        </Image>
                        <TextBlock
                            Margin="4,0,0,0"
                            Text="{Binding Name}"
                            TextTrimming="CharacterEllipsis" />
                    </StackPanel>
                </DataTemplate>
            </grids:TreeListBox.ItemTemplate>
            <grids:TreeListBox.ItemContainerStyle>
                <Style TargetType="{x:Type grids:TreeListBoxItem}">
                    <Setter Property="IsExpanded" Value="{Binding Path=Expanded}" />
                    <Setter Property="Visibility" Value="{Binding Path=Visible, Converter={StaticResource BoolToVis}}" />
                </Style>
            </grids:TreeListBox.ItemContainerStyle>
        </grids:TreeListBox>

 For testing purpose I've also tried changing the line to

 <Setter Property="IsExpanded" Value="True" />

 But all treeitems are collapsed. I'm aware of the IsExpandedBinding property but this doesn't seem work with binding to ReactiveProperty which requires binding to a nested property. For example the binding would look like

public ReactiveProperty<bool> Expanded { get; set;} = new ReactiveProperty<bool>();

 IsExpandedBinding="{Binding Expanded.Value}"

 That's why I wanted to do this in the style of treelistboxitem.