"Good" ways of copying files preserve the "last modified" time of both the original file and the copy (well, it'd have to be a particularly bad form of copying to modify the "last modified" time of the original, eh?). I suggest you test File::Copy to verify that it does this in your specific configuration.

One problem under Windows is that different file systems have different resolutions for their file time stamps (or, that is my guess at the source of the problem). This can mean that the two files end up with slightly different time stamps. I haven't investigated this fully but did put an "off by one (minute)" hack into some code I wrote that compared file modification times in Windows. ):

        - tye (but my friends call me "Tye")