Hi, My Performance MX mouse just arrived. Although it seems to work fine but I see a huge crack on the darkfield sensor. See the Images: http://img16.yfrog.com/img16/5349/p1040337n.jpg http://img269.yfrog.com/img269/668/p1040334p.jpg Is it normal or should I get the mouse replaced? Can someone having this mouse please confirm if its defect or not? Please just turn over your mouse to check, I'd really appreciate. Many Thanks!