I think the bar graphs are not displaying proportionately to the percentages. If, for example, you find a position that is 100% black, there is still a small area of white and one of gray displayed. Example:
http://www.redhotpawn.com/gamesexplorer/index.php?movelist=c2c4e7e5b1c3g8f6g2g3d7d5c4d5f6d5f1g2d5c3&flip=1&co=-&u=-1&c=1900