New bug in 3.1.4: Event Registrations are not matched to existing Contacts

I have reported this in the forum (http://forum.civicrm.org/index.php/topic,13609.msg58269.html#msg58269) though not got any response.

I upgraded to 3.1.4 just before launching registrations for a new Event. All online registrations are not syncing to existing Contacts but creating new Contacts. That is, user fills in their details and a new Civi Contact is created for them rather than updating the exisitng contact details.
This worked on prior versions. I have not knowingly changed anything else

I've been able to duplicate this error on the demo site with the following actions:

• log on
• create a user
• log off
• register that user for an event

there are now two users, not one

(do a full text search on "lionel" on the demo site and you will see what i did)

Lionel.