When two contacts have the same openid, login using that openid fails

I had an accidentally created duplicate user in the system, that is, two contacts with the same openid. trying to log in using that openid caused the following error:

DB Error: already exists
Datenbank-Errorcode: Duplicate entry 'http://www.myopenid.com/server-*********-***** for key 2, 1062

I stared out some parts of the URI since i suppose it's an openid session token or some such.

Now, I fugured deleting the duplicate would fix the error. But then she gets:

Datenbank-Errorcode: Cannot add or update a child row: a foreign key constraint fails (`db91024_14/civicrm_acl_cache`, CONSTRAINT `FK_civicrm_acl_cache_contact_id` FOREIGN KEY (`contact_id`) REFERENCES `civicrm_contact` (`id`) ON DELETE CASCADE), 1452

It seems that the ACL cache can't deal with deletion of contacts too well.