NW6.5sp5, nss 5a

I've looked through the previous posts about this issue, but I haven't
found a definitive answer.

User has had an account on the system for years.
Only recently has he had files start disappearing from Windows Explorer
when looking at his home directory.
Using a Mac, all the files are visible.
We had him use the Mac to create a new folder and drop the missing files
into it.
Then he could see them on the Windows machine.
Now the files have disappeared from Explorer again.
Not all of them have been accessed by him in the meantime.