Key TakeawaysChipotle Mexican Grill shares continued to fall Monday after setting a record high when shareholders approved a 50-to-1 stock split in June.The Mexican fast-food chain has been accused by some customers of reducing the size of its burrito bowls, which CEO Brian Niccol denies.Shares of Chipotle have lost about 13% since reaching an all-time high last month, but still have added almost a third of their value this year. Chipotle Mexican Grill (CMG) was one of the worst-performing stocks in the S&P ...