Sequelizejs executes 2 inserts

I'm trying to execute a insert, and sequelize is executing the insert twice.

First insert: only with userid, updatedAt, createdAt,

Second Insert: the other fields

Console Result

#Insert car: {"name":"CarTest","description":"desc","myNumber":123,"id":"","UserId":1}
Executing (undefined): INSERT INTO `Cars` (`UserId`,`updatedAt`,`createdAt`) VALUES (1,'2014-09-17 22:31:49','2014-09-17 22:31:49');
Executing (undefined): INSERT INTO `Cars` (`id`,`name`,`description`,`myNumber`,`createdAt`,`updatedAt`,`UserId`) VALUES (DEFAULT,'CarTest','desc',123,'2014-09-17 22:31:49','2014-09-17 22:31:49',1);
saved: {"name":"CarTest","description":"desc","myNumber":123,"id":39,"UserId":1,"updatedAt":"2014-09-17T22:31:49.000Z","createdAt":"2014-09-17T22:31:49.000Z"}

My model Car.js

module.exports = function(sequelize, DataTypes) {
    var Car = sequelize.define('Car', {
        name: {
            type: DataTypes.STRING,
        },
        description: {
            type: DataTypes.STRING,
        },
        myNumber: {
            type: DataTypes.BIGINT,
        },
    },{
          classMethods: {
          associate: function(models) {
              Car.belongsTo(models.User,{ foreignKeyConstraint: true})
          }
      }
    });
    return Car;
};

My controller

var mycar =  db.Car.build(req.body);
mycar.setUser(req.user);

console.log("#Insert car: "+ JSON.stringify(mycar));
mycar.save().success(function(entity) {
    res.json(entity);
    console.log("saved: "+ JSON.stringify(entity));
}).error(function(error){
    console.log("error: "+ error);
});

package.json

"mysql": "^2.5.0",
"connect-session-sequelize": "^2.0.0",

What I'm doing wrong? Why is sequelize executing the save in separated inserts?