I suspect it has something to do with NTFS updating access times by default. So every time you do anything with a file, it gets its access time updated (not modification time, access time). I don't have windows to test on, but you could try the suggestions [1][2] below.
[1] http://msdn.microsoft.com/en-us/library/ms940846(v=winembedd...
[2] http://oreilly.com/pub/a/windows/2005/02/08/NTFS_Hacks.html (#8)
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