I tried to register on http://www.commandlinefu.com/users/openid with my Stack Exchange OpenID. It logged me in, but not completely.
The full error message is:
Detected an attempt to send an assertion when the identifier (https://openid.stackexchange.com/) is not owned by the logged in user.
I don't know where it could come from (CommandLineFu, SE, whatever).
I tried with Firefox & Opera 29, both at home and at work.
If anyone could confirm, we will at least be sure it is not a temporary issue.