File permission lost

Hi,

Sometimes when I'm working on a file, located in my Documents folder, I
suddenly loose permissions on the file. Obviously, the file is still there.
For a short while that is, because after about two minutes, the file is
suddenly gone. The file is only opened by one application.
When this happens, all file permissions are gone. I am logged on as an
Administrator account. I've tried logging on to the built in Administrator
account, and even that account has no permissions to access or edit the file,
let alone it's permissions.
As you might understand, this is highly annoying when you're trying to work.
This usually happens once every day, at different times of the day.
The only possible thing I can think of, is that it is the Desktop Search
service, which is indexing the file at the exact time that I save it.

Has anyone encountered a problem like this? Does anyone know what might
cause it, and more importantly, how to solve it?

Regards,
MueR