Rails - comments w actions_as_nested_set - when deleting a dependent record, destruction data is deleted

Question

Rails - comments w actions_as_nested_set - when deleting a dependent record, destruction data is deleted

I have the following models:

class Group < ActiveRecord::Base
    has_many :threads, :dependent => :destroy

class Thread < ActiveRecord::Base
    has_many :comments, :as => :commentable, :dependent => :destroy

 class Comment < ActiveRecord::Base
    belongs_to :commentable, :polymorphic => true
    acts_as_nested_set

The problem I am facing is that the user deletes the group, all kinds of comments are broken or deleted. I looked at the logs, and this is what happens:

Comment Load (0.8ms)  SELECT "comments".* FROM "comments" WHERE ("comments".commentable_id = 101 AND "comments".commentable_type = 'Thread') ORDER BY comments.created_at DESC
AREL (0.9ms)  DELETE FROM "comments" WHERE ("comments"."lft" > 649 AND "comments"."rgt" < 650)
AREL (0.4ms)  UPDATE "comments" SET "lft" = ("lft" - 2) WHERE ("lft" > 650)
AREL (0.5ms)  UPDATE "comments" SET "rgt" = ("rgt" - 2) WHERE ("rgt" > 650)
AREL (0.2ms)  DELETE FROM "comments" WHERE ("comments"."id" = 381)
AREL (0.4ms)  DELETE FROM "comments" WHERE ("comments"."lft" > 645 AND "comments"."rgt" < 646)
AREL (0.4ms)  UPDATE "comments" SET "lft" = ("lft" - 2) WHERE ("lft" > 646)
AREL (0.4ms)  UPDATE "comments" SET "rgt" = ("rgt" - 2) WHERE ("rgt" > 646)
AREL (0.2ms)  DELETE FROM "comments" WHERE ("comments"."id" = 380)
AREL (0.3ms)  DELETE FROM "comments" WHERE ("comments"."lft" > 648 AND "comments"."rgt" < 651)
AREL (0.3ms)  UPDATE "comments" SET "lft" = ("lft" - 4) WHERE ("lft" > 651)
AREL (0.3ms)  UPDATE "comments" SET "rgt" = ("rgt" - 4) WHERE ("rgt" > 651)
AREL (0.2ms)  DELETE FROM "comments" WHERE ("comments"."id" = 379)
AREL (0.3ms)  DELETE FROM "comments" WHERE ("comments"."lft" > 644 AND "comments"."rgt" < 647)
AREL (0.4ms)  UPDATE "comments" SET "lft" = ("lft" - 4) WHERE ("lft" > 647)
AREL (0.4ms)  UPDATE "comments" SET "rgt" = ("rgt" - 4) WHERE ("rgt" > 647)
AREL (0.2ms)  DELETE FROM "comments" WHERE ("comments"."id" = 378)
AREL (0.4ms)  DELETE FROM "comments" WHERE ("comments"."lft" > 642 AND "comments"."rgt" < 643)
AREL (0.8ms)  UPDATE "comments" SET "lft" = ("lft" - 2) WHERE ("lft" > 643)
AREL (0.4ms)  UPDATE "comments" SET "rgt" = ("rgt" - 2) WHERE ("rgt" > 643)
AREL (0.2ms)  DELETE FROM "comments" WHERE ("comments"."id" = 377)
AREL (0.7ms)  DELETE FROM "comments" WHERE ("comments"."lft" > 641 AND "comments"."rgt" < 652)
AREL (0.9ms)  UPDATE "comments" SET "lft" = ("lft" - 12) WHERE ("lft" > 652)
AREL (0.9ms)  UPDATE "comments" SET "rgt" = ("rgt" - 12) WHERE ("rgt" > 652)
AREL (0.3ms)  DELETE FROM "comments" WHERE ("comments"."id" = 376)
AREL (0.4ms)  DELETE FROM "threads" WHERE ("threads"."id" = 101)
AREL (0.4ms)  DELETE FROM "groups" WHERE ("groups"."id" = 57)

Is this normal behavior for actions as nested? I would only expect DELETE FROM COMMENTS, where Comment.id = XXXX. But instead, it all happens, and the comment entries break.

Has anyone seen this before?

thank

UPDATE w What is used to prevent deep nesting:

  after_save :ensure_max_nestedset_level
  def ensure_max_nestedset_level
    if self.level > 2
      self.move_to_child_of(parent.parent)
    end
  end