什么是带有点的DataTable列名，使它们不适合WPF的DataGrid控件？

Run this, and be confused:

运行这个，并混淆：

<Window x:Class="Data_Grids.MainWindow"
        xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel>
        <DataGrid
        Name="r1"
              ItemsSource="{Binding Path=.}">
        </DataGrid>
        <DataGrid
        Name="r2"
              ItemsSource="{Binding Path=.}">
        </DataGrid>
    </StackPanel>
</Window>
<Windo