If I use exclude I can lose my information

If I use exclude I can lose my information. Here is what happens in my auth middleware:

         17         if session_key:
         18             try:
         19                 user = User.objects.exclude('crm_data').get(id=session_key)
         20                 import ipdb; ipdb.set_trace()
         21             except User.DoesNotExist:
         22                 user = None
         23             else:
    ---> 24                 if not user.is_active:
         25                     ...

    # crm_data was not loaded, but was replaced with default value
    ipdb> user.crm_data
    CrmData(notes=[], tags=[])

    # but there are values in `crm_data` in the DB
    ipdb> User.objects.get(id=session_key).crm_data
    CrmData(notes=[], tags=[u'test'])

    # if I accidentally save the instance
    ipdb> user.save()
    ...

    # data in the db is lost
    ipdb> User.objects.get(id=session_key).crm_data
    CrmData(notes=[], tags=[])