Update should cover everything on operating system.
Windows 7 Start Menu > Control Panel > System and Security > Administrative Tools > Task Scheduler >
(Upper left corner) Task Scheduler (Local) > Task Scheduler Library > Microsoft > Windows > Diagnosis > (Right pane)
enable all task history > Disabled…… or try this
….. Click on view Task Scheduler (Local) scroll down to change an existing task and follow command.
Do you have windows 7 business or home and is it an upgrade from XP or Vista?
Maybe Dennis will step in here….
As you can see this PC is set on enable and I don't have the disappearing problems.