Sequelize bug 2

bug.js

const Sequelize = require('sequelize');
const config = require('./config')();

const {DataTypes} = Sequelize;

const db = new Sequelize({
	database: config.postgres.database,
	username: config.postgres.user,
	password: config.postgres.password,
	host: config.postgres.host,
	port: config.postgres.port,
	dialect: 'postgres',
	logging: false
});

db.parents = db.define('Parent', {
	_id: {
		type: DataTypes.INTEGER,
		primaryKey: true,
		autoIncrement: true
	},
	somefield: {type: DataTypes.TEXT, unique: true}
}, {
	timestamps: false,
	tableName: 'parents'
});

db.children = db.define('Child', {
	_id: {
		type: DataTypes.INTEGER,
		primaryKey: true,
		autoIncrement: true
	}
}, {
	timestamps: false,
	tableName: 'children'
});

db.parentToChild = db.define('parentToChild', {
	parentId: {type: DataTypes.INTEGER},
	childId: {type: DataTypes.INTEGER},
	additional: {type: DataTypes.TEXT}
}, {
	timestamps: false,
	tableName: 'parentToChild'
});

db.parents.belongsToMany(db.children, {
	as: 'children',
	through: 'parentToChild',
	foreignKey: 'parentId',
	otherKey: 'childId',
	timestamps: false
});

db.parents.hasMany(db.parentToChild, {
	as: 'additionals',
	foreignKey: 'parentId'
});

db.parentToChild.removeAttribute('id');

db.parentToChild.belongsTo(db.children, {
	as: 'child',
	foreignKey: 'childId',
	targetKey: '_id'
});


(async () => {
	try {
		await db.transaction(async (transaction) => {
			await db.parents.truncate({transaction});
			await db.parentToChild.truncate({transaction});
			await db.children.truncate({transaction});

			const {_id: parentId} = await db.parents.create(
				{somefield: 'somevalue'},
				{transaction}
			);
			const {_id: childId} = await db.children.create({}, {transaction});

			await db.parentToChild.create({
				parentId,
				childId,
				additional: 'some additional info'
			}, {transaction});

			const parent = await db.parents.findOne({
				where: {somefield: 'somevalue'},
				include: [{
					model: db.parentToChild,
					as: 'additionals',
					required: true,
					include: [{
						model: db.children,
						as: 'child',
						required: true
					}]
				}],
				transaction,
				logging: console.log
			});

			console.log(require('util').inspect(parent.toJSON(), false, null));
		});
	} catch (err) {
		console.log(err.stack);
	}
})();