This has happened twice now in three months:

After rebooting, ALL the pinned items from my Windows Explorer taskbar jumplist are gone. Also, recent items from Windows Explorer are much fewer, only one or two if I remember correctly. After the first time I re-pinned the items I wanted, but about a month later it happened again. I re-pinned

All other pinned items in other jumplists (e.g. Word) are fine and have never disappeared. Googling for the problem showed that ccleaner can affect this, but I personally do NOT use any cleaners or related progs on this machine.

I also think that both times it happened it was after a windows update, although I can't recall what kind of update it was.

After each time, Little Registry Editor showed invalid references in HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\RecentDocs , but I had NOT used it prior to the deletions.

Any ideas on why this happens and how to prevent it?