IntegrityError when saving user with username=email

Question

I have modified my application, so that when a new user is registered, it's username and email are the same. But when a new user is created, I'm getting IntegrityError : (1062, "Duplicate entry '[email protected]' for key 'username'"), still the user is created correctly.
Function register_new in which a new user is created ('temp_data' is a dict from form.cleaned_data) :

def register_new(request):
    data = request.session['temp_data']
    email = data['email']
    password1 = data['password1']
    userdata = {'email': email, 'password1': password1}
    backend = request.session['backend']
    user = backend.register(request, userdata)

,here's the registration.backend register function, that creates new user :

def register(self, request, userdata):
    logging.debug("backend.register")
    logging.debug(userdata)
    username, email, password = userdata['email'], userdata['email'], userdata['password1']
    if Site._meta.installed:
        site = Site.objects.get_current()
    else:
        site = RequestSite(request)         
    new_user = RegistrationProfile.objects.create_inactive_user(username, email, password, site)
    return new_user

Traceback :

File "/home/rails/site-packages/django/core/handlers/base.py" in get_response
  92.                 response = callback(request, *callback_args, **callback_kwargs)
File "/home/rails//registration/views.py" in register_new
  112.     user = backend.register(request, userdata)
File "/home/rails/registration/backends/default/__init__.py" in register
  21.                                                                     password, site)
File "/home/rails/site-packages/django/db/transaction.py" in _commit_on_success
  240.                 res = func(*args, **kw)
File "/home/rails/registration/models.py" in create_inactive_user
  73.         new_user = User.objects.create_user(username, email, password)
File "/home/rails/site-packages/django/contrib/auth/models.py" in create_user
  105.         user.save()
File "/home/rails/site-packages/django/db/models/base.py" in save
  410.         self.save_base(force_insert=force_insert, force_update=force_update)
File "/home/rails/site-packages/django/db/models/base.py" in save_base
  495.                     result = manager._insert(values, return_id=update_pk)
File "/home/rails/site-packages/django/db/models/manager.py" in _insert
  177.         return insert_query(self.model, values, **kwargs)
File "/home/rails/site-packages/django/db/models/query.py" in insert_query
  1087.     return query.execute_sql(return_id)
File "/home/rails/site-packages/django/db/models/sql/subqueries.py" in execute_sql
  320.         cursor = super(InsertQuery, self).execute_sql(None)
File "/home/rails/site-packages/django/db/models/sql/query.py" in execute_sql
  2369.         cursor.execute(sql, params)
File "/home/rails/site-packages/django/db/backends/util.py" in execute
  19.             return self.cursor.execute(sql, params)
File "/home/rails/site-packages/django/db/backends/mysql/base.py" in execute
  84.             return self.cursor.execute(query, args)
File "build/bdist.linux-x86_64/egg/MySQLdb/cursors.py" in execute
  173.             self.errorhandler(self, exc, value)
File "build/bdist.linux-x86_64/egg/MySQLdb/connections.py" in defaulterrorhandler
  36.     raise errorclass, errorvalue

Exception Type: IntegrityError at /register_new/
Exception Value: (1062, "Duplicate entry '[email protected]' for key 'username'")

I've googled for solutions and found many different including deleting/syncing tables, catching the IntegrityError in different places, changing decoding fields for table columns (I've tried setting to utf8_bin but no results). How to fix this problem ?

Table structure :

http://i27.tinypic.com/dotmjs.png
http://i32.tinypic.com/1zq79tj.png

I've found this ticket at django docs : http://code.djangoproject.com/ticket/3083 But there should be 2 models created at the same time. In my case nothing like this takes place I guess :/

UPDATE Model :

class User(models.Model):
    username = models.CharField(_('Email'), max_length=30, unique=True, help_text=_("Required. 30 characters or fewer."))
    first_name = models.CharField(_('first name'), max_length=30, blank=True)
    last_name = models.CharField(_('last name'), max_length=30, blank=True)
    email = models.EmailField(_('e-mail address'), blank=True)
    password = models.CharField(_('password'), max_length=128, help_text=_("Use '[algo]$[salt]$[hexdigest]' or use the <a href=\"password/\">change password form</a>."))
    is_staff = models.BooleanField(_('staff status'), default=False, help_text=_("Designates whether the user can log into this admin site."))
    is_active = models.BooleanField(_('active'), default=True, help_text=_("Designates whether this user should be treated as active. Unselect this instead of deleting accounts."))
    is_superuser = models.BooleanField(_('superuser status'), default=False, help_text=_("Designates that this user has all permissions without explicitly assigning them."))
    last_login = models.DateTimeField(_('last login'), default=datetime.datetime.now)
    date_joined = models.DateTimeField(_('date joined'), default=datetime.datetime.now)

Answer 1

I'd catch MySQLdb error in this init file of registration backend, since it is first to cause problems :

import MySQLdb

(...)
    new_user = None
    try:    
        new_user = RegistrationProfile.objects.create_inactive_user(username, email, password, site)
    except MySQLdb.IntegrityError:
        pass