1. configure "Show only task from the current screen" to checked in single montior make sure the icon is appear in single monitor. 2. connected another monitor 3. then you will found the taskmanager is all disappear event the window is on the current screen. this will also happened if you configure taskmanager in multiple screen, then disconnected the other screen. the task in taskmanager will all disappear
*** This bug has been marked as a duplicate of bug 373075 ***