customizing notifications in system tray

I have changed the setting for some of the icons in my system tray to be 'Always show', instead of 'Hide when inactive'. Occasionally, some of these revert back to 'Hide when active'. I have not identified any pattern in when this happens. Does anyone know of any way to verify that the change has been made? That is, what is changed when the customization change is made? I've checked the registry for changes, and the only change is some Random Number Generator.confused