I'm not sure why. I didn't study it before it happened and now I'm not sure I can replicate it. Maybe after I start a new game I'll keep track of every time I exit the game (which saves it) and every hot sync and see if at some point it duplicates itself. Until then it'll remain a mystery!! Luckily there is a work around as long as you either pause before hot syncing or notice it right away so that your save game isn't so old all your villagers wind up as dead