Behaviour of grouped notification on Android 7

I create several notifications like this:

public class NotificationCreator {
    Context context;
    int c = 0;

    public NotificationCreator(final Context context) {
        this.context = context;
    }

    void create() {

        String text = "" + c  + " " + new Date().toGMTString();

        // Intent
        Intent intent = new Intent(context, SecondActivity.class);
        intent.putExtra(SecondActivity.KEY, text);
        Intent[] intents = new Intent[1];
        intents[0] = intent;
        PendingIntent pendingIntent = PendingIntent.getActivities(
                context,
                c,
                intents,
                PendingIntent.FLAG_CANCEL_CURRENT);

        // Build notification
        NotificationCompat.Builder builder = new NotificationCompat.Builder(context);
        builder.setSmallIcon(R.drawable.notification);
        builder.setContentTitle("Test");
        builder.setContentText(text);
//        builder.setGroup("");
        builder.setContentIntent(pendingIntent);
        Notification notification = builder.build();

        // Send notification
        NotificationManager notificationManager = (NotificationManager)
                context.getSystemService(NOTIFICATION_SERVICE);

        notificationManager.notify(c, notification);

        c++;
    }
}

The outcome on Android 7 is:

The system has grouped all notifications.

When I set explicitly on the builder:

 builder.setGroup("myGroup");

the outcome is:

The notifications are not grouped, but all shown individually, despite all having the same group key.

1. Is this the expected behaviour?

2. In the first case (grouped), can I determine what happens when the user clicks on the grouped notification? The individual intents seem to be ignored and just the app opened.