Why are my Windows 8 WPF radio buttons all out of whack?

In Windows 8 RTM with VS2012 RTM I noticed my WPF app was giving me deformed radio buttons so I decided to create a sample to see if I was doing something wrong.

Here's the entire XAML App :

<Window x:Class="WpfApplication1.MainWindow" 
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" SizeToContent="WidthAndHeight">
    <Grid>
        <StackPanel Margin="20">
            <RadioButton Content="Option 1" GroupName="1"/>
            <RadioButton Content="Option 2" GroupName="2"/>
            <RadioButton Content="Option 3" GroupName="3"/>
        </StackPanel>
    </Grid>
</Window>

Here I have the DPI settings set to 100%, which is actually NOT the default in Windows 8 (well at least for my 1920x1200 screen it isn't). You'll see the radio buttons are perfect.

This is the same exact application with DPI settings at 125% which is the default DPI for my screen resolution.

Here's 150%

You can see the inner circles aren't centered within the outer circle and it looks TERRIBLE. System applications with radio buttons are fine - but my WPF 4.5 app is not. Once again this sample app is 100% RTM bits and from scratch under Win 8.

Is it just all broken or is there a way to fix this (apart from insisting people put 100% DPI scaling).

Was really hoping Win8 would have gone a long way for high res screens and scaling issues like this, but something simple is badly