This probably applies to a lot more of our forms, but reporting it for these pages since they're the ones I'm talking about...

On http://musicbrainz.org/edit/artist/add.html?initial_name=adjpwnejpewk you can tab through the entire page, type, artist name, guess case, guess sort name, copy sortname, dates, etc.

On http://test.musicbrainz.org/artist/create it goes artist name, sort name, comment, etc. There's no way to access the guess case stuff by tabbing, and if you click, it interrupts the position, so pressing tab again won't take you to the next field, it'll take you to the first field on the page (which the search box at the top of the page)