MultipleObjectsReturned: get() returned more than one Variable

[papousek]

Internal Server Error: /flashcards/practice/
Traceback (most recent call last):
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/core/handlers/base.py", line 111, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/utils/decorators.py", line 105, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/lazysignup/decorators.py", line 45, in wrapped
    return func(request, *args, **kwargs)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/db/transaction.py", line 394, in inner
    return func(*args, **kwargs)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso_flashcards/views.py", line 272, in practice
    saved_answers = _save_answer(request, answers)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso_flashcards/views.py", line 350, in _save_answer
    db_answer.save()
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/db/models/base.py", line 589, in save
    force_update=force_update, update_fields=update_fields)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/db/models/base.py", line 626, in save_base
    update_fields=update_fields, raw=raw, using=using)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/dispatch/dispatcher.py", line 198, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso/django/util.py", line 16, in wrapper
    signal_handler(*args, **kwargs)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso_models/models.py", line 886, in insert_ab_values
    instance.save()
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/db/models/base.py", line 589, in save
    force_update=force_update, update_fields=update_fields)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/db/models/base.py", line 626, in save_base
    update_fields=update_fields, raw=raw, using=using)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/dispatch/dispatcher.py", line 198, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso/django/util.py", line 16, in wrapper
    signal_handler(*args, **kwargs)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso_models/models.py", line 874, in update_predictive_model
    item_asked=instance.item_asked_id)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso/models/prediction.py", line 33, in predict_and_update
    environment, data, prediction, user, item, correct, time, **kwargs)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso/models/prediction.py", line 231, in update_phase
    environment.write('current_skill', current_skill, user=user, item=item, time=time)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/proso_models/models.py", line 378, in write
    variable = Variable.objects.get(**data)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/db/models/manager.py", line 92, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/var/www/slepemapy.cz/virtualenv/geography-production-2/lib/python2.7/site-packages/django/db/models/query.py", line 361, in get
    num if num <= MAX_GET_RESULTS else 'more than %s' % MAX_GET_RESULTS
MultipleObjectsReturned: get() returned more than one Variable -- it returned 2!

Request repr():
<WSGIRequest
path:/flashcards/practice/,
GET:<QueryDict: {u'all': [u'True'], u'stats': [u'True'], u'contexts': [u'["europe"]'], u'avoid': [u'[350]'], u'limit': [u'2'], u'types': [u'["state"]'], u'categories': [u'[]']}>,