beforeValidate didn't get called in cascade validation

class Parent {
  static hasMany = [children:Child]
}

class Child {
  static belongsTo = [parent:Parent]

  String name

  def beforeValidate() {
    name = 'hard coded in beforeValidate'
  }
}

def save = {
  def parentInstance = new Parent(params)
  parentInstance.addToChildren(new Child(name:params.name))
  if (parentInstance.save(flush: true)) {
    ...
  }
  else {
    ...
  }
}