QWindow::showFullScreen doesn't work well with window expand button on Mac OS 10.8

Resize from -1x-1 to 200x100
Resize from 640x480 to 200x100
  KeyPress key=0x00000041=(A)  status: isFullScreen=0 windowState=0
  KeyPress key=0x01000013=()=UP
showFullScreen - Resize from 200x100 to 1280x800
status: isFullScreen=1 windowState=1
  KeyPress key=0x00000042=(B)  status: isFullScreen=1 windowState=1
  KeyPress key=0x01000015=()=DOWN
showNormal - status: isFullScreen=0 windowState=0
Resize from 1280x800 to 200x100
  KeyPress key=0x00000043=(C)  status: isFullScreen=0 windowState=0
Resize from 200x100 to 1280x800
  KeyPress key=0x00000044=(D)  status: isFullScreen=1 windowState=1
  KeyPress key=0x01000015=()=DOWN
showNormal - status: isFullScreen=0 windowState=0
  KeyPress key=0x00000045=(E)  status: isFullScreen=0 windowState=0
  KeyPress key=0x01000013=()=UP
showFullScreen - status: isFullScreen=1 windowState=1
Resize from 1280x800 to 200x100
  KeyPress key=0x00000046=(F)  status: isFullScreen=0 windowState=0

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
CONFIG += release
HEADERS = fullscreen.h
SOURCES = fullscreen.cpp

#include <QMainWindow>
class QEvent;

class TopWindow : public QMainWindow {
    Q_OBJECT
  public:
    TopWindow();  // creates subwidgets and does show()
  private:
    bool event(QEvent *event);
};

// test Qt full screen functions:
// can we enter and exit full screen mode well?

#include <iostream>
#include <QApplication>
#include <QKeyEvent>
#include <QLabel>

#include "fullscreen.h"

TopWindow::TopWindow() {
  QLabel *label = new QLabel(this);
  label->setText("xyz");
  show();
}

bool TopWindow::event(QEvent *event) {
  switch (event->type()) {
    case QEvent::KeyPress:
      {
        QKeyEvent *key_event = static_cast<QKeyEvent *>(event);
        int key = key_event->key();
        printf("  KeyPress key=0x%08x=(%c)", key, key);
        switch (key) {
          case Qt::Key_Up:
            printf("=UP\nshowFullScreen - ");
            showFullScreen();
            printf("status: isFullScreen=%d windowState=%d\n", isFullScreen(),
                windowState().testFlag(Qt::WindowFullScreen));
            return true;  // we handled the event
            break;
          case Qt::Key_Down:
            printf("=DOWN\nshowNormal - ");
            showNormal();
            printf("status: isFullScreen=%d windowState=%d\n", isFullScreen(),
                windowState().testFlag(Qt::WindowFullScreen));
            return true;  // we handled the event
            break;
          default:
            printf("  status: isFullScreen=%d windowState=%d\n", isFullScreen(),
                windowState().testFlag(Qt::WindowFullScreen));
            break;
        }
        break;
      }
    case QEvent::Resize:
      {
        QResizeEvent *resize_event = static_cast<QResizeEvent *>(event);
        printf("Resize from %dx%d to %dx%d\n",
            resize_event->oldSize().width(), resize_event->oldSize().height(),
            resize_event->size().width(), resize_event->size().height());
        break;
      }
    default: break;
  }
  return false;  // we didn't handle the event
}

int main(int argc, char **argv) {
  QApplication app(argc, argv);
  TopWindow top;
  app.exec();
}