After closing main window of ACDSee icon or RBTray will stay in the tray area.
If any window was hidden by RBTray to tray icon, and then restored without click on tray icon (i.e. by some internal event) - icon will be show in the tray until you move mouse over this icon.
Toi eliminate this behavior I'd have to check existance of all hidden windows by timer or some other event. I don't like such unnecessary load.