title: Django form validation errors being duplicated
body: <p>I have the following form in django:</p>
  
  <pre><code>class UserEmailRegistrationForm(forms.Form):
      password = forms.PasswordField(max_length=32, label=_('Password'),
                                     validators=[validators.validate_password])
      email = forms.EmailField(label=_('Email'), 
                               validators=[validators.validate_email])
      first_name = forms.CharField(max_length=35, label=_('First name'), 
                                   validators=[validators.validate_name])
      last_name = forms.CharField(max_length=35, label=_('Last name'), 
                                  validators=[validators.validate_name])
  </code></pre>
  
  <p>Most validators are custom, but <code>validate_email</code> is as seen in <code>django.core.validators</code>. Also, here's the relevant part of my view:</p>
  
  <pre><code>form = UserEmailRegistrationForm(PUT)       
      # Validate incoming data
      if not form.is_valid():
          return HttpResponse(form.errors.as_json(), 
                              content_type='application/json', status=422)
  </code></pre>
  
  <p>All validators are working fine, but I get <code>Enter a valid email address.</code> twice in <code>form.errors</code> when I pass along an invalid email address. Here's the response I get:</p>
  
  <pre><code>{"email": [{"message": "Enter a valid email address.", "code": "invalid"}, {"message": "Enter a valid email address.", "code": "invalid"}]}
  </code></pre>
  
  <p>What could be causing this and how can I resolve it?</p>