That's described in documentation on rich:listShuttle: http://jboss.org/file-access/default/members/jbossrichfaces/freezone/docs/devguide/en/html/listShuttle.html#d0e42464 I've notified documentation team to add this information to picklist page where it's missing. Thank you for reporting the issue!
I doubt this will be addressed in JSF 2.0. In fact, you'll get exactly the same issue trying to get h:selectManyMenu to work without equals().
And, BTW, just to remind: you have to override hashCode() also.
It seemed to work without overriding hashCode() but I will ensure I do that now.