Hi John,
We're aware of a bug that means under certain circumstances, this can happen. We're working on a fix that will let you correct the database as part of an upgrade, and we hope to have it ready in a week or so.
In the mean time, if you're happy working directly with your database you could remove the duplicate record yourself. I can post further instructions if that would be helpful, but you will need direct access to the database to make the change.
Simon