QDialog not showing close button on Mac

[manojmka]

Qt4.4.1
I am facing a problem of missing close button on QDialog on Mac. Buttons are visible and working on windows but not on Mac.

I am creating a QDialog as follows:

FormHtmlDisplay newFeatures(this);
newFeatures.setFixedSize(200,50);
newFeatures.exec();

FormHtmlDisplay newFeatures(this);
newFeatures.setFixedSize(200,50);
newFeatures.exec();

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Constructor for FormHtmlDisplay is as follows:

FormHtmlDisplay::FormHtmlDisplay(QWidget *parent):QDialog(parent)
{
  init();
}

FormHtmlDisplay::FormHtmlDisplay(QWidget *parent):QDialog(parent)
{
  init();
}

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I have not changed any properties in designer for QDialog in designer for FormHtmlDisplay class. Can some body help me why it is not showing close button on top left on Mac?