Mixin trouble with Spine.js

gistfile1.coffee

class AjaxHelpers
  unbind_ajax_handlers: (item) ->
    item.unbind('ajaxSuccess')
    item.unbind('ajaxError')

  ajax_error_handler: (item, xhr) ->
    if xhr.responseText
      alert("#{key.split('_').join(' ')} #{value}") for key, value of jQuery.parseJSON(xhr.responseText)
    else
      alert("There was a problem submitting this update to the server.")
    @unbind_ajax_handlers(item)

class Edit extends Spine.Controller
  @include AjaxHelpers

  submit: (e) =>
    e.preventDefault()
    @errors.empty()
    previous = @item.dup()
    if @item.fromForm(e.target).save()
      @stack.new.active()
      @item.bind 'ajaxSuccess', (sent, record, statusText, xhr) =>
        $('.flashMessage p').stop().text("Entry saved").fadeOut(2500)
        @unbind_ajax_handlers(@item)
      @item.bind 'ajaxError', (record, xhr, statusText, body) =>
        @ajax_error_handler(@item, xhr)
        @item.updateAttributes(rating: previous.rating, timestamp: previous.timestamp)
        @item.save()
        Spine.Ajax.disable ->
          previous.destroy()
    else
      error_text = @item.fromForm(e.target).validate()
      @errors.append($('<li/>', {html: error_text}))