Are you sure it's not just an illusion of movement, a la, a 'wagon-wheel effect'?

It's possibly just an artist oversight though - there are actually several small errors in background object placement throughout the game (such as the infamous 'floating bottle' on the ground in Pearl Lane in Ul'dah, and the book buried in the mantlepiece in the tavern at the Observatorium in Coerthas), so it's probably not intentional, but just a minor mistake that wasn't picked up in time.