I have been experiencing a problem with the author nickname that is displayed after upgrading to WordPress 2.8.4. Before I upgraded the nickname that was showing up in the user profile was shown as the author. After the upgrade "admin" is shown as the nickname for a particular author even though the old nickname is still shown in the user's profile. Changing the username does not have an effect on the issue.
I conclude that it must have something to do with the update since I have not changed anything besides updating.