I have several open applications running. The icons display on the taskbar as running. After some time the icons will disappear. They are still running in task manager but are notvisible on the task bar. I can reboot andopen again and they will show.
I actually see this on my work PC (windows XP). I've never really bothered with it, but sometimes a browser session or a some running app will disappear when I minimize it. To fix it, I just alt-tab to the program, and it pops back up on the task bar as it brings the window back up.