почему во время второго Insert, id сходит с ума?

CREATE TABLE `devices`.`common` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `Department` INT NULL,
  `InvNumber` VARCHAR(45) NULL,
  `Name` VARCHAR(45) NULL,
  `Got` INT NULL,
  `WrittenOff` INT NULL,
  `Price` INT NULL,
  PRIMARY KEY (`id`))
ENGINE = MyISAM
DEFAULT CHARACTER SET = utf8;
INSERT INTO devices.common (department,InvNumber,Name,Got,writtenoff,price)
    SELECT
    department,
    InvNumber,
    Name,
    Got,
    WrittenOff,
    Price
    FROM devices.main;

INSERT INTO devices.common (department,InvNumber,Name,Got,writtenoff,price)
    SELECT
    department,
    InvNumber,
    Name,
    Got,
    WrittenOff,
    Price
    FROM devices.cheap;