Binding Mongoose models save method inside async.auto (NodeJs)

Right now I'm working with both mongoose 3.1.1 and async 0.1.22. But when I tried to save Mongoose models instance inside async.auto it just stopped working.

See the following example and try it by yourself:

mongoose = require 'mongoose'
async = require 'async'
Schema = mongoose.Schema
ObjectId = Schema.ObjectId

mongoose.connect "mongodb://localhost:27017/async-test"

SmthSchema = new Schema
  data : type: String

mongoose.model 'Smth', SmthSchema
Smth = mongoose.model 'Smth'

test1 = (next) ->
  console.log '  test 1'
  smth = new Smth data: 'some data'

  async.auto
    first: (callback) ->
      smth.save callback
    second: ['first', (callback) ->
      console.log '  it works!'
      callback()]
    next

test2 = (next) ->
  console.log '  test 2'
  smth = new Smth data: 'some data'

  async.series [
    smth.save.bind smth
    (callback) ->
      console.log '  it works!'
      callback()
  ], next

test3 = (next) ->
  console.log '  test 3'
  context =
    save: (callback) -> callback null

  async.auto
    first: context.save.bind context
    second: ['first', (callback) ->
      console.log '  it works!'
      callback()]
    next

test4 = (next) ->
  console.log '  test 4'
  smth = new Smth data: 'some data'

  async.auto
    first: smth.save.bind smth
    second: ['first', (callback) ->
      console.log '  it works!'
      callback()]
    next

console.log 'running all tests'
async.series [test1, test2, test3, test4], (err) ->
  console.log err || 'all works!'

Resulting output:

running all tests
  test 1
  it works!
  test 2
  it works!
  test 3
  it works!
  test 4

smth.save.bind smth binds save function to the object it shall save. It works great in async.series and async.parallel, but not in async.auto.

async.auto saves the object to database, but it looses callback and processing stops. But does anybody have any idea why it happens?

The strangest thing is than i never had any problems neither with binding anything else inside of async.auto nor with binding Mongoose save method in any other context.

I already looked into async code, but I still have no idea what's wrong. Now I'm planning to write an issue about it on github.

Added 20.09.12: I replaced save function with validate function and all worked great:

running all tests
  test 1
  it works!
  test 2
  it works!
  test 3
  it works!
  test 4
  it works!
all works!

So the problem deeply connected to mongoose save function.

It looks like async.auto breaks somewhere when it works with Mongoose method save. But I can't understand where and why.