A Funny Thing Happened on the Way to the Terrorist Hunt

The darndest thing happened just a few minutes ago. After arriving home from a 14 hour workday, I turned on my Xbox 360 and popped in Rainbow Six: Vegas 2, looking forward to an hour or so of unwinding before heading to bed with a book. Apparently an update had been released so I let the game download the update and restart which took all of 45 seconds and when the game reached the menu screen I was greeted with a surprise.

"Achievement Unlocked: Private First Class"

Now, unless my Xbox has taken to playing with itself when I'm not around, (I always knew it was a dirty machine), there's really no logical explanation for receiving an achievement upon loading the menu screen. What's far more bizarre is the fact that I am far, FAR past the rank of Private. In fact, on my achievement list for R6: Vegas, the date listed for the Officer achievement is 4/14/2008 and date for the Private First Class achievement is 4/23/2008, (screenshot coming tomorrow). In case you don't understand that paradox let me explain; in order to reach Officer status, you must pass through the rank of Private first. Essentially what I have done is equivalent to being thirty years old and at my next birthday instead of turning thirty-one, I turn five.

Has anyone else had issues similar to this?