Cannot remove entities then flush on a "Tree" structured entity

gistfile1.aw

<?php

/**
 * @Gedmo\Tree(type="nested")
 *
 * @ORM\Entity(repositoryClass="Gedmo\Tree\Entity\Repository\NestedTreeRepository")
 * @ORM\Table(name="node_tree")
 * @ORM\InheritanceType("JOINED")
 * @ORM\DiscriminatorColumn(name="discr", type="string")
 * @ORM\DiscriminatorMap({"node" = "Node", "sub_node" = "SubNode"})
 * @ORM\HasLifecycleCallbacks
 */
class Node implements MyNodeInterface
{
    /**
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue
     */
    private $id;

    /**
     * @Gedmo\TreeLeft
     * @ORM\Column(name="lft", type="integer")
     */
    private $lft;

    /**
     * @Gedmo\TreeLevel
     * @ORM\Column(name="lvl", type="integer")
     */
    private $lvl;

    /**
     * @Gedmo\TreeRight
     * @ORM\Column(name="rgt", type="integer")
     */
    private $rgt;

    /**
     * @Gedmo\TreeRoot
     * @ORM\Column(name="root", type="integer", nullable=true)
     */
    private $root;

    /**
     * @Gedmo\TreeParent
     * @ORM\ManyToOne(targetEntity="Node", inversedBy="children",cascade={"remove"})
     * @ORM\JoinColumn(name="parent_id", referencedColumnName="id",onDelete="set null")
     */
    private $parent;

    /**
     * @ORM\OneToMany(targetEntity="Node", mappedBy="parent",cascade={"remove"})
     * @ORM\OrderBy({"lft" = "ASC"})
     */
    private $children;
}