The master in your story is evolution, the slave is the brain. Both want different things. We normally identify with the brain, though all identities are basically social signals.

Also, pleasure and pain are no different from the other goals of the slave. The master definitely can't step in and decide not to impose pain on a particular occasion just because doing so would increase status or otherwise serve the master's values. If it could, torture wouldn't cause pain.

Also, math is an implausible goal for a status/sex/power seeking master to instill in slave. Much more plausibly, math and all the diverse human obsessions are misfirings of mechanisms built by evolution for some other purpose. I would suggest maladaptive consequences of fairly general systems for responding to societal encouragement with obsession because societies encourage sustained attention to lots of different unnatural tasks, whether digging dirt or hunting whales or whatever in order to cultivate skill and also to get the tasks themselves done. We need a general purpose attention allocator which obeys social signals in order to develop skills that contribute critically to survival in any of the vast number of habitats that even stone-age humans occupied.

Since we are the slave and we are designing the AI, ultimately, whatever we choose to do IS extracting our preferences, though it's very possible that our preferences give consideration to the master's preferences, or even that we help him despite not wanting to for some game theoretical reason along the lines of Vinge's meta-golden rule.

Why the objection to randomness? If we want something for its own sake and the object of our desire was determined somewhat randomly we want it all the same and generally do so reflectively. This is particularly clear regarding romantic relationships.

Once again game-theory may remove the randomness via trade between agents following the same decision procedure in different Everett branches or regions of a big world.