The change user in RCS is the full user name for a registered and logged in user. However it seems, that by creating a cookie with a Wiki name before creating a user, the wiki name from the old preference style cookie is used.
I've checked the revision files and the user is indeed the full name.
This is somewhat annoying as full name and Wiki name do not necessarily match, so you cant jump directly to the user pages anymore. (No link is being created)

I am displaying the last 3 days of changes on the front page, so it has quite a large impact on easiness of use for me.