post method in generic class based view is not called upon form submission in Django?

Question

I have a written a mixin that overrides the POST and get_from_kwargs of CreateView. I am doing AJAX submission of my form. I see that get_from_kwargs is called by printing on the console. But none of the other methods such as post,form_valid or form_invalid is being called. I have placed print statements in these methods but none of them is being called.

Here is my mixin:

class PendFormMixin(object):
    form_hash_name = 'form_hash'
    pend_button_name = 'pend'

    def get_form_kwargs(self):
        """
        Returns a dictionary of arguments to pass into the form instantiation.
        If resuming a pended form, this will retrieve data from the database.
        """
        pk_form = self.kwargs.get('pk', None)
        form_hash = None
        if pk_form: 
            form_data = PendedForm.objects.get(pk=pk_form)
            form_hash = form_data.hash
            print "form_hash", form_hash
        if form_hash:
            import_path = self.get_import_path(self.get_form_class())
            print import_path
            print self.get_pended_data(import_path, form_hash)
            return {'data': self.get_pended_data(import_path, form_hash)}
        else:
            print "called in kwargs"
            # print super(PendFormMixin, self).get_form_kwargs()
            return super(PendFormMixin, self).get_form_kwargs()

    def post(self, request, *args, **kwargs):
        """
        Handles POST requests with form data. If the form was pended, it doesn't follow
        the normal flow, but saves the values for later instead.
        """
        self.object = None
        if self.pend_button_name in self.request.POST:
            print "here"
            form_class = self.get_form_class()
            print form_class
            form = self.get_form(form_class)
            # print "form is ", form
            self.form_pended(form)
            return super(PendFormMixin, self).post(request, *args, **kwargs)
        else:
            print "here in post"
            return super(PendFormMixin, self).post(request, *args, **kwargs)

# Custom methods follow
    def get_import_path(self, form_class):
        return '{0}.{1}'.format(form_class.__module__, form_class.__name__)

    def get_form_hash(self, form):
        content = ','.join('{0}:{1}'.format(n, form.data[n]) for n in form.fields.keys())
        return md5(content).hexdigest()

    def form_pended(self, form):
        import_path = self.get_import_path(self.get_form_class())
        form_hash = self.get_form_hash(form)
        pended_form = PendedForm.objects.get_or_create(form_class=import_path,
                                                       hash=form_hash)
        for name in form.fields.keys():
            pended_form[0].data.get_or_create(name=name, value=form.data[name])
        return form_hash

    def get_pended_data(self, import_path, form_hash):
        print "import_path is", import_path
        print "form_hash is", form_hash
        # data = PendedValue.objects.filter(import_path=import_path, form_hash=form_hash)
        data = PendedValue.objects.filter(form__form_class=import_path, form__hash=form_hash)
        print "data ", data
        return dict((d.name, d.value) for d in data)

Here is my view:

class ArticleCreateView(PendFormMixin, CreateView):
      form_class = ArticleForm
      model = Article
      template_name = "article_create.html"
      # success_url = reverse_lazy('blog_create')
      success_url = '/admin'

      def form_valid(self, form):
        """
        If the request is ajax, save the form and return a json response.
        Otherwise return super as expected.
        """
        if self.request.is_ajax():
            self.object = form.save()
            time.sleep(5)
            print "here"
            return HttpResponse(json.dumps("success"),
                mimetype="application/json")
        if self.pend_button_name in self.request.POST:
            print "in the form_valid"
            return 
        print "in the form_valid"
        return super(ArticleCreateView, self).form_valid(form)

      def form_invalid(self, form):
        """
        We haz errors in the form. If ajax, return them as json.
        Otherwise, proceed as normal.
        """
        print "self is ", self.request.POST
        if self.request.is_ajax():
            return HttpResponseBadRequest(json.dumps(form.errors),
                mimetype="application/json")
        if self.pend_button_name in self.request.POST:
            print "in the form_invalid"
            return redirect('/admin')
        return super(ArticleCreateView, self).form_invalid(form)

unable to figureout what is going wrong. It used to work previously, before I used the mixin. but by introducing the above mixin, the code does not work any more.