Get a catchable error when trying to find an entity by composite PK which contains association key in the identity map

use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;

/**
 * @ORM\Entity
 */
class Foo
{
    /**
     * @ORM\Column(type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue
     */
    public $id;

    /**
     * @ORM\Column(type="string", nullable=true)
     */
    public $name;

    /**
     * @ORM\OneToMany(targetEntity="FooHasBar", mappedBy="foo", cascade={"persist", "remove", "merge"})
     */
    public $children;

    public function __construct()
    {
        $this->children = new ArrayCollection();
    }
}

/**
 * @ORM\Entity
 */
class Bar
{
    /**
     * @ORM\Column(type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue
     */
    public $id;

    /**
     * @ORM\Column(type="string", nullable=true)
     */
    public $name;
}

/**
 * @ORM\Entity
 */
class FooHasBar
{
    /**
     * @ORM\Id
     * @ORM\ManyToOne(targetEntity="Foo", inversedBy="children")
     * @ORM\JoinColumn(name="foo_id", referencedColumnName="id", nullable=false)
     */
    public $foo;

    /**
     * @ORM\Column(type="integer")
     * @ORM\Id
     */
    public $mode;

    /**
     * @ORM\ManyToOne(targetEntity="Bar")
     * @ORM\JoinColumn(name="bar_id", referencedColumnName="id", nullable=false)
     */
    public $bar;

    public function __construct(Foo $foo, Bar $bar, $mode)
    {
        $this->foo = $foo;
        $this->bar = $bar;
        $this->mode = $mode;
    }
}