Device.OpenUri and WP8

I noticed that this method failed to launch custom Uri such as driving directions (ms-drive-to:?) on Windows Phone 8. It looks like it is calling WebBrowserTask task rather than using the system launcher. I was wondering if this was by design limited to only web links? I had to create Uri launch method in Xamarin.Form.Labs IDevice interface so I could bypass this. Basically the same functionality on iOS and Android but for WP8 it is not limited to http/https schemes.

    public async Task<bool> LaunchUriAsync(Uri uri)
    {
        return await Windows.System.Launcher.LaunchUriAsync(uri);
    }

Based on the Device.OpenUri documentation I would think this is a bug on WP8.