Django user admin interface operations will be failed

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For all users created with the login dialog all operations in the Django user admin interface will be failed with following exception (example for user 1):

Request Method: POST Request URL: http://<host>:<port>/admin/auth/user/1/ Django Version: 1.4 Exception Type: IntegrityError Exception Value:

update or delete on table "auth_user_groups" violates foreign key constraint "authusergroups_ptr_id_refs_id_5cdfc23b7859c44e" on table "askbot_groupmembership" DETAIL: Key (id)=(1) is still referenced from table "askbot_groupmembership".

Exception Location: /usr/lib/python2.7/site-packages/django/db/backends/postgresql_psycopg2/base.py in _commit, line 235 Python Executable: /usr/bin/python Python Version: 2.7.3

Why conflicts the Askbot user administration with the underlying Django user administration? Is this a known issue?