Tray icon freezes when unread count is reduced to 0

[alastairb]

Mail Notification 5.4, KDE 4.3.2, Kubuntu 9.10

Everything works fine with mail-notification for my Gmail and IMAP accounts except when 0 unread messages are encountered. When I start mail-notification and I have no unread messages, I see no tray icon. I assume that is the expected behaviour. And when messages arrive, the appropriate icon and message number appear in the system tray. However, when I handle the messages, reducing the unread count to zero, the icon "freezes" -- it does not go away, it displays the old inaccurate unread message count, and the right mouse button no longer works. Other aspects of mail notification continue to work, such as the notification box when a new message arrives, but the system tray icon never unfreezes.