When I first set up my blog I decided to disable the author page using the checkbox on the Indexation page. This does a 301 back to the home page.
Then I read your post on using author=rel and figured that I should enable the author page again. I also decided to create a 2nd author called Guest for guest posts and syndicated articles.
However, the redirect still happens for my initial user name but the author page for Guest works fine.
I tried re-enabling the date based archives as well and enabling the indexing of the author pages, but that doesn't do anything (I didn't think it would). I also checked my .htaccess file to see if there is anything in there that might cause this, but there is only the standard WP code.