After restarting my laptop, I have observed that some of the files in my hard drive disappeared on their own, and they seem to reappear after multiple restarts. This has happened mostly to files which have been downloaded from the internet (video/movie files and folders), but there is not a pattern as such to this incident, and it happens randomly.
After a bit of searching I tried to locate the files from the terminal, and found that the files are still there, but all of them have their permissions lost and shown as '?'.
If I changed the permissions manually, the missing files would probably show in the GUI file browser, but if I haven't done anything why should I revert to the old permissions?
I am running Ubuntu 12.10. Please help me to understand this problem.