regression: Dialog can't cover entire screen under Qt5, but can be under Qt4

#include <QApplication>

#include <QtDeclarative>

#include <QWidget>

QWidget* subWidget;

class MyWidget
  : public QWidget
{
public:
  MyWidget(QWidget* parent = 0)
    : QWidget(parent)
  {
    subWidget = new QWidget(this, Qt::FramelessWindowHint | Qt::Dialog);

    subWidget->show();
  }

  void resizeEvent(QResizeEvent* event)
  {
    subWidget->setGeometry(QRect(pos(), event->size()));
  }
};

//////////////////////////////////////////////////////////////////////////////
int main(int argc, char* argv[])
{
  QApplication app(argc, argv);

  QApplication::setAttribute(Qt::AA_NativeWindows);

  MyWidget widget;

  widget.setStyleSheet("background:\"red\"");

  widget.showFullScreen();

  subWidget->setStyleSheet("background:\"green\"");

  subWidget->setAutoFillBackground(true);

  return app.exec();
}