anchor.diff:      NCount = lists:foldl(fun(N, AccN) ->
                                    AccN + node_size(N)
                            end, 0, ChildNodes),
  -    {nil, 1 + NCount, ItemCount + length(KeyList), Interval, ChildNodes}.
  +    % hash the bucket now:
  +    Hash = run_inner_hf(ChildNodes, Config#mt_config.inner_hf),
  +    {Hash, 1 + NCount, ItemCount + length(KeyList), Interval, ChildNodes}.
   
   -spec build_childs([{I::intervals:continuous_interval(), Count::non_neg_integer(),
                        mt_bucket()}], mt_config(), Acc::[mt_node()]) -> [mt_node()].
  
positive.code: 
  %% @doc Hashes a leaf with the given (sorted!) bucket.
  -spec run_leaf_hf(mt_bucket(), intervals:interval(), LeafHf::leaf_hash_fun())
          -> mt_node_key().
  run_leaf_hf(Bucket, I, LeafHf) ->
      ?DBG_ASSERT(lists:ukeysort(1, Bucket) =:= Bucket),
      Hash = LeafHf(Bucket, I),
      Size = erlang:bit_size(Hash),
      <<SmallHash:Size/integer-unit:1>> = Hash,
      SmallHash.
  
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  
negative.code: gen_hash_node({_OldHash, ICnt, Bucket, Interval},
                _InnerHf, LeafHf, true, CleanBuckets) ->
      % leaf node, keep_bucket true
      {Bucket1, Hash} = run_leaf_hf(Bucket, Interval, LeafHf),
      {Hash, ICnt, ?IIF(CleanBuckets, [], Bucket1), Interval}.
  
  %% @doc Hashes an inner node based on its childrens' hashes.
  