stackpanel possibly incorrect orientation within datatemplate ?

[germgerm]

i have a layout that works as expected when not using data binding, but when converting to a bound layout things stack vertically instead of horizontally and I don't understand why the bound version has the VERTICAL layout that it does - I assume it has something to do with the inner stackpanel being within itemscontrol/datatemplate

Logical (unbound) layout :

        <Border BorderBrush="Chartreuse" BorderThickness="2" Margin="2">
            <StackPanel Orientation="Horizontal" Width="100" HorizontalAlignment="Left">
        
                <Border BorderBrush="Blue" BorderThickness="2" Margin="2">
                    <StackPanel Orientation="Vertical">
                        <Border BorderBrush="Red" BorderThickness="2" Margin="2">
                            <TextBlock Text="Value 1"></TextBlock>
                        </Border>
                        <Border BorderBrush="Red" BorderThickness="2" Margin="2">
                            <TextBlock Text="Value 2"></TextBlock>
                        </Border>
                        <Border BorderBrush="Red" BorderThickness="2" Margin="2">
                            <TextBlock Text="Value 3"></TextBlock>
                        </Border>
                    </StackPanel>
                </Border>

                <Border BorderBrush="Blue" BorderThickness="2" Margin="2">
                    <StackPanel Orientation="Vertical">
                        <Border BorderBrush="Red" BorderThickness="2" Margin="2">
                            <TextBlock Text="Value 1"></TextBlock>
                        </Border>
                        <Border BorderBrush="Red" BorderThickness="2" Margin="2">
                            <TextBlock Text="Value 2"></TextBlock>
                        </Border>
                        <Border BorderBrush="Red" BorderThickness="2" Margin="2">
                            <TextBlock Text="Value 3"></TextBlock>
                        </Border>
                    </StackPanel>
                </Border>

            </StackPanel>
        </Border>

    </StackPanel>
</Border>

Bound Layout :

<Border Margin="2" BorderBrush="Coral" BorderThickness="2">
    <StackPanel Name="Fretboard" Orientation="Vertical">
        <TextBlock Text="{Binding Name}" HorizontalAlignment="Center" VerticalAlignment="Center" />
        
        <Border Margin="2" BorderBrush="Chartreuse" BorderThickness="2">
            <StackPanel Orientation="Horizontal" Width="100" HorizontalAlignment="Left">
                <ItemsControl ItemsSource="{Binding data2d}">
                    <ItemsControl.ItemTemplate>
                        <DataTemplate>
                            <Border Margin="2"
                                    BorderBrush="Blue" BorderThickness="2">
                                <StackPanel Orientation="Vertical">
                                    <ItemsControl ItemsSource="{Binding  }">
                                        <ItemsControl.ItemTemplate>
                                            <DataTemplate>
                                                <Border Margin="2"
                                                        BorderBrush="Red" BorderThickness="2">
                                                    <TextBlock Text="{Binding Value}"></TextBlock>
                                                </Border>
                                            </DataTemplate>
                                        </ItemsControl.ItemTemplate>
                                    </ItemsControl>
                                </StackPanel>
                            </Border>
                        </DataTemplate>
                    </ItemsControl.ItemTemplate>
                </ItemsControl>
            </StackPanel>
        </Border>

    </StackPanel>
</Border>

[germgerm]

I looked at itemsrepeater which does what I want - it is deprecated but got me going in the right direction

        <Border Margin="2" BorderBrush="Chartreuse" BorderThickness="2">
            <StackPanel Orientation="Horizontal" Width="100" HorizontalAlignment="Left">
                <ItemsControl ItemsSource="{Binding Fretboard}">
                    <ItemsControl.ItemsPanel>
                        <ItemsPanelTemplate>
                            <StackPanel Orientation="Horizontal"/>
                        </ItemsPanelTemplate>
                    </ItemsControl.ItemsPanel>
                    <ItemsControl.ItemTemplate>
                        <DataTemplate>
                            <Border Margin="2"
                                    BorderBrush="Blue" BorderThickness="2">
                                <StackPanel Orientation="Vertical">
                                    <ItemsControl ItemsSource="{Binding  }">
                                        <ItemsControl.ItemTemplate>
                                            <DataTemplate>
                                                <Border Margin="2"
                                                        BorderBrush="Red" BorderThickness="2">
                                                    <TextBlock Text="{Binding xValue}"></TextBlock>
                                                </Border>
                                            </DataTemplate>
                                        </ItemsControl.ItemTemplate>
                                    </ItemsControl>
                                </StackPanel>
                            </Border>
                        </DataTemplate>
                    </ItemsControl.ItemTemplate>
                </ItemsControl>
            </StackPanel>
        </Border>

    </StackPanel>
</Border>