c# – 样式未正确应用

<Style TargetType="ComboBox">
    <Setter Property="VerticalContentAlignment" Value="Center" />
    <Setter Property="Foreground" Value="Black" />
    <Setter Property="Margin" Value="5" />
</Style>
<Style TargetType="TextBlock">
    <Setter Property="VerticalAlignment" Value="Center" />
    <Setter Property="Margin" Value="5" />
    <Setter Property="FontSize" Value="20" />
    <Setter Property="FontWeight" Value="Bold" />
    <Setter Property="Foreground" Value="White" />
</Style>
<Style TargetType="TextBox">
    <Setter Property="VerticalContentAlignment" Value="Center" />
    <Setter Property="Margin" Value="5" />
    <Setter Property="Height" Value="35" />
    <Setter Property="FontSize" Value="20" />
</Style>
[...]
<ComboBox SelectedIndex="{Binding Path=BirthdayDay,UpdateSourceTrigger=PropertyChanged,FallbackValue=0}" ItemsSource="{Binding Path=Days,UpdateSourceTrigger=PropertyChanged}" />
<ComboBox SelectedIndex="{Binding Path=BirthdayMonth,FallbackValue=0}" ItemsSource="{Binding Path=Months,UpdateSourceTrigger=PropertyChanged}" />
<ComboBox SelectedIndex="{Binding Path=BirthdayYear,FallbackValue=0}" ItemsSource="{Binding Path=Years,UpdateSourceTrigger=PropertyChanged}" />

结果很混乱：

它是否以某种方式与TextBlock样式发生冲突？
由于应用了FontWeight,似乎有连接？！

注意：

我可以看到Binding不同的唯一“明显”差异：

Day Year是整数的集合,而Month是字符串的集合？！