I don't think class challenges should be available during the tutorial dungeons (I mean Vince's Vault, Thousand Cuts, and The BAAdlands), as it allows you to immediately unlock all the classes by completing their bronze challenges. Then thief silver is immediately available, so a player could have the balanced dagger before he has even gotten past these tutorials. I think they should be unlocked when you unlock the real dungeons.
Anyone agree? Disagree? Think they should be moved to a different place?