Mac OSX: QDialogButtonBox buttons doesn't change focus correctly

Buttons focus is not updated correctly when using standard buttons Ok,Cancel and Help in QDialogBox and change focus with the Tab key. Button focus is enabled once but not disabled from Help or Cancel button. Ok button focus is disabled correctly. See attachment screenshot_dialogbox.png.

To repoduce the issue we need Keyboard all controls enabled in OS X:
System preferences > keyboard > keyboard shortcuts
under "Full Keyboard Access..."
select the "All controls" radio button. See attachment screenshot_keyboard_settings.png

#include <QApplication>
#include <QDialog>
#include <QDialogButtonBox>

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	QDialog dialog;
	new QDialogButtonBox(QDialogButtonBox::Ok
			|QDialogButtonBox::Cancel
			|QDialogButtonBox::Help
			,Qt::Horizontal
			,&dialog);
	dialog.show();
	return a.exec();
}

There's no issue on Qt 4.8.5.