What I know:
File Shadowing is a term for the way which Windows archives its files. When you save a file it could easily double in size or be cut to half its size.This is not a progressive change. You can't continue to cut your files in half by repated saves. It wills stay between the high and low file size as it is archives, assuming nothing else is changed in the file.
What I don't know:
What logic does Windows use for this?
Why does it do it?
Does Winndows create a backup of the file, or duplicate information?