XAML - Objekty v druhem "gridu" se neukazuji

Zdravim, ucim se XAML ale narazil jsem na problem. Kdyz definuju druhy grid, tak se mi v nem neukazou objekty ale v prvnim ano. Cim je to zpusobene? Predem dekuji za odpovedi.

Screen: Wry3Zvl.png

<StackPanel>                  
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="75"></ColumnDefinition>
                        <ColumnDefinition Width="75"></ColumnDefinition>
                        <ColumnDefinition Width="75"></ColumnDefinition>
                        <ColumnDefinition></ColumnDefinition>
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="53"></RowDefinition>
                        <RowDefinition Height="75"></RowDefinition>
                    </Grid.RowDefinitions>
                    <Rectangle Fill="#333333" HorizontalAlignment="Left" Height="128" Grid.RowSpan="2" VerticalAlignment="Top" Width="480" Grid.ColumnSpan="4"/>
                </Grid>
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="75"></ColumnDefinition>
                        <ColumnDefinition Width="75"></ColumnDefinition>
                        <ColumnDefinition Width="75"></ColumnDefinition>
                        <ColumnDefinition></ColumnDefinition>
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="53"></RowDefinition>
                        <RowDefinition Height="75"></RowDefinition>
                    </Grid.RowDefinitions>
                    <Rectangle Fill="#333333" HorizontalAlignment="Left" Height="128" Grid.RowSpan="2" VerticalAlignment="Top" Width="480" Grid.ColumnSpan="4"/>
                </Grid>
            </StackPanel>