I was roux. I am now user456. what happened? (yes I have flushed my cache etc).
This was actually a site-wide problem affecting the entire SE network.
It happened because they changed the authentication mechanism so that it's easier for people to sign in on multiple SE sites (some members here, myself included, participate on several). Not all OpenID providers were affected, but myopenid (the one you're using) was one of them.
The issue didn't seem to affect people who changed their user name after registering, but for those people who use any of the affected OpenID providers and whose names were directly derived from their OpenID (never changed) - their display names disappeared.
It is possible that they'll fix this, but seeing as how it was a one-time incident, I doubt it; it'll be easier for you to edit your profile and manually change your name, as hobodave suggests.