title: Form not valid. ID: Select a valid choice. That choice is not one of the available choices
body: <p>When I run this code, even the whole data is correct.
  <code>demobilized_formset.is_valid()</code> gives me <code>False</code> and <code>demobilized_formset.errors</code> gives <code>{u'id': [u'Select a valid choice. That choice is not one of the available choices.']}</code></p>
  
  <p>I don't know why an error comes to <code>id</code> as <code>{u'id': [u'Select a valid choice. That choice is not one of the available choices.']}</code></p>
  
  <p><strong>managers.py</strong></p>
  
  <pre><code>class DemobilizedEmployee(models.Manager):
      use_for_related_fields = True
      def get_queryset(self):
          # When I use filter instead of exclude it works fine.
          return super(DemobilizedEmployee, self).get_queryset().exclude(
              demobilized_date=None)
  </code></pre>
  
  <p><strong>models.py</strong></p>
  
  <pre><code>class PurchasedEmployees(AuditDeleteSafeModel):
      purchase = models.ForeignKey(Purchase)
      employee = models.ForeignKey(Employee)
      category = models.CharField(max_length=32)
      mobilized_date = models.DateField()
      demobilized_date = models.DateField(null=True, blank=True)
      period_worked = models.PositiveSmallIntegerField(null=True, blank=True)
  
      mobilized_emp = MobilizedEmployee()
      demobilized_emp= DemobilizedEmployee()
      objects =  # Is also an custom Manager which changes deleted=True in Abstract Model
      class Meta:
          db_table = 'purchased_employees'
  </code></pre>
  
  <p><strong>forms.py</strong> </p>
  
  <pre><code>class DetailMobilizeForm(forms.ModelForm):
      class Meta:
          model = PurchasedEmployees
          fields = ('employee', 'category', 'mobilized_date',
                    'demobilized_date', 'period_worked')
  DetailMobilizeInlineFormSet = modelformset_factory(
      PurchasedEmployees, can_delete=False, extra=0, form=DetailMobilizeForm)
  </code></pre>
  
  <p><strong>views.py</strong></p>
  
  <pre><code>def update_demobilize_emp(request, id=None):
      purchase = get_object_or_404(Purchase, id=id) if id else Purchase()
      demobilized_queryset = PurchasedEmployees.demobilized_emp.filter(
          purchase=purchase)
  
      if request.POST:
          demobilized_formset = DetailMobilizeInlineFormSet(
              data=request.POST,
              prefix='demobilized_form')
  
          if demobilized_formset.is_valid():
              demobilized_formset.save()
              status_code, res = 200, {'status': 'true'}
          else:
              for form in demobilized_formset:
                  import ipdb; ipdb.set_trace()
              errors = {}
              errors[demobilized_formset.prefix + '_errors'] =\
                  demobilized_formset.errors
              status_code, res = 202, {'error': errors , 'status': 'false'}
  
          return HttpResponse(
              json.dumps(res), content_type='application/json',
              status=status_code)
  
      else:
          demobilized_formset = DetailMobilizeInlineFormSet(
              queryset=demobilized_queryset,
              prefix='demobilized_form')
  
      return render_to_response(
          'purchase/update_demobilized_employees.html', {
          'demobilized_formset': demobilized_formset, 'purchase': purchase},
          context_instance=RequestContext(request))
  </code></pre>
  
  <p><strong>template</strong></p>
  
  <pre><code>&lt;div class="field"&gt;
      {{ demobilized_formset.management_form }}
      &lt;div class="box"&gt;
        {% for forms in demobilized_formset.forms %}
        &lt;div class="box_item"&gt;
            {{ forms }}
            &lt;br class="clear"&gt;
        &lt;/div&gt;
        {% endfor %}
    &lt;/div&gt;
  </code></pre>
  
  <p>And </p>
  
  <pre><code>...
  
  &lt;label for="id_demobilized_form-0-period_worked"&gt;Period worked:&lt;/label&gt;
  &lt;input id="id_demobilized_form-0-period_worked" type="number" value="100" name="demobilized_form-0-period_worked" min="0"&gt;
  &lt;input id="id_demobilized_form-0-id" type="hidden" value="8" name="demobilized_form-0-id"&gt;
  &lt;ul class="errorlist"&gt;
      &lt;li&gt;Select a valid choice. That choice is not one of the available choices.&lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>