On Mac OS X 10.9.5, run QSystemTrayIcon example included in the Qt installation. Click on the icon shown on the menu bar to activate the menu. Then click elsewhere to deactiviate it. The icon goes blank on the menu bar. If you click on the blank space again, the icon re-appears.

Another issue I'm having with QSystemTrayIcon on Mac is, setting a different pixmap for the icon never worked. On Mac OS X the guidance for menu bar icon is it should invert color when activated. So you should supplied a second icon for activated state. I try icon.addPixmap for various mode and state, none worked.