manytomany relations fail on select with multiple records

Userpro\Entity\Group:
    type: entity
    table: userpro_group
    fields:
        id:
            id: true
            type: integer
            column: id
            generator:
                strategy: AUTO
        name:
            name: name
            type: string
            lenght: 100
        permission:
            name: permission
            type: string
            lenght: 100
    lifecycleCallbacks: {  }

Userpro\Entity\User:
  type: entity
  table: userpro_user
  fields:
    id:
      id: true
      type: integer
      column: id
      generator:
        strategy: AUTO
    name:
      name: username
      type: string
      lenght: 100
  manyToMany:
    group:
      targetEntity: Userpro\Entity\Group
      cascade: {  }
      mappedBy: null
      joinTable:
        name: userpro_users_groups
        joinColumns:
          -
            name: user_id
            referencedColumnName: id
        inverseJoinColumns:
          -
            name: group_id
            referencedColumnName: id
      orderBy: null
  lifecycleCallbacks: {  }

$group = new Userpro\Entity\Group;
$group->setName('test');
$group->setPermission('test');

$em->persist($group);
$em->flush();

$user = new Userpro\Entity\User;
$user->setName('samuel');
$user->addGroup($em->find('Userpro\Entity\Group', 1));

$em->persist($user);
$em->flush();

$dql = "SELECT	u, g
		FROM	Userpro\Entity\User u
		JOIN	u.group g
		ORDER
			BY	u.name ASC
";

$result = $em->createQuery($dql);
$users = $result->getResult();

echo '<pre>';
if($users) {
	foreach($users as $user) {
		echo $user->getName() . "\n";

		foreach($user->getGroup() as $group) {
			echo "\t" . $group->getName() . "\n";
		}

		echo "\n";
	}
}