CupertinoDynamicColor not working for text style within a theme in Flutter

Question

Currently I've got a problem with the dark mode for iOS in Flutter. I'm using a CupertinoApp with a CupertinoTheme.

With CupertinoDynamicColor.withBrightness() it's possible to define colors for dark and light theme. This is working for example for the navigation bar (barBackgroundColor), but not for the textTheme.

Someone already ask a similar question in the flutter repository but I don't know how to do this with a theme. Maybe you can help me there.

Example code:

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return CupertinoApp(
      title: 'Flutter Demo',
      theme: CupertinoThemeData(
        barBackgroundColor: const CupertinoDynamicColor.withBrightness(
          color: Colors.blue,
          darkColor: Colors.red,
        ),
        textTheme: CupertinoTextThemeData(
          textStyle: TextStyle(
            color: const CupertinoDynamicColor.withBrightness(
              color: Colors.blue,
              darkColor: Colors.red,
            ),
          ),
        ),
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return CupertinoPageScaffold(
      navigationBar: CupertinoNavigationBar(middle: Text('Test')),
      child: Text('Test Text'),
    );
  }
}