Windows Phone 7 Popup problem

I'm having this really frustrating problem that when I show a popup that has a ListBox with RadioButtons, the first item shows up cropped. I've spent almost two hours trying to fix it but I just can't. I know it's a really stupid problem, but I've ran out of ideas.

Any ideas on how to fix this? Basically the popup shows up when I press some button, and this is how it shows up:

And this is the XAML:

<Popup Grid.Row="1" Grid.RowSpan="4" x:Name="popupDateSelection" HorizontalAlignment="Center" Width="400">
    <Grid>
        <Border BorderBrush="White" BorderThickness="4" Width="400">
            <Border.Background>
                <SolidColorBrush Color="Black" Opacity=".9" />
            </Border.Background>
            <ListBox>
                <ListBoxItem>
                    <ListBoxItem.Content>
                        <RadioButton Content="Item 1" Checked="radioButtonDates_Checked" />开发者_JS百科;
                    </ListBoxItem.Content>
                </ListBoxItem>
                <ListBoxItem>
                    <ListBoxItem.Content>
                        <RadioButton Content="Item 2" Checked="radioButtonDates_Checked" />
                    </ListBoxItem.Content>
                </ListBoxItem>
                <ListBoxItem>
                    <ListBoxItem.Content>
                        <RadioButton Content="Item 3" Checked="radioButtonDates_Checked" />
                    </ListBoxItem.Content>
                </ListBoxItem>
                <ListBoxItem>
                    <ListBoxItem.Content>
                        <RadioButton Content="Item 4" Checked="radioButtonDates_Checked" />
                    </ListBoxItem.Content>
                </ListBoxItem>
            </ListBox>
        </Border>
    </Grid>
</Popup>

Thanks.

<Grid Margin="0,20"> maybe?