Is the shadow file on the SD card? If that's where it is, it's because of our Macs habit of trying to play nice with things that are not native to their OS.
The same thing will show up if you place a W&^d*ws formatted floppy in a Mac, save something on it, and then take it back to a W&^d*ws machine. Those little shadow files, from what has been explained to me by my Mac Guru, are the Mac's way of trying to play nice.
Does that help?