It wouldn't supprse me at all if (in efforts to make a more elaborate product in these quasi-modernistic over-saturated times) Microsoft did put some silly option like an option to remove (delete!) files on your system if the file is not used for a preset amount of time. (a stupid option, not to mention harmfull)
If this is a case please let us know.
(If they (Microsoft) changed from that fine-working "Find" option from Win98 Explorer to that "let's buggy" XP style, then everything is possible (so I ask))
(I guess that HD sound when you left your computer (Win XP) untouched for a while is defragmenting or file sysem maintanance or something, but still... I ask)