Django 站点,使用 python-social-auth 登录豆瓣,时不时出现 AuthStateMissing 异常, 是怎么回事?

为了方便自己看RSS, 最近用Django做了个RSS聚合以及推送Kindle的小网站:

http://feedfree.me/

我使用python-social-auth做豆瓣OAuth2登录, 大部分时候正常, 但时不时会出现这个异常:

File "/srv/env/feedfree/local/lib/python2.7/site-packages/social/apps/django_app/views.py", line 21, in complete
redirect_name=REDIRECT_FIELD_NAME, *args, **kwargs)

File "/srv/env/feedfree/local/lib/python2.7/site-packages/social/actions.py", line 44, in do_complete
*args, **kwargs)

File "/srv/env/feedfree/local/lib/python2.7/site-packages/social/strategies/base.py", line 71, in complete
return self.backend.auth_complete(*args, **kwargs)

File "/srv/env/feedfree/local/lib/python2.7/site-packages/social/backends/oauth.py", line 345, in auth_complete
data=self.auth_complete_params(self.validate_state()),

File "/srv/env/feedfree/local/lib/python2.7/site-packages/social/backends/oauth.py", line 307, in validate_state
raise AuthStateMissing(self, 'state')

AuthStateMissing: Session value state missing.

我怀疑是session的什么设置不对, 但是看了python-social-auth的文档, 没找到相关信息.
有人遇到过类似的问题么?