I hate to admit it, but I always dread getting paired up with mentors in duty roulette, since most of the ones I've met have been asocial and/or passive aggressive (not even sparing a "hello" when you greet them). They usually want to get the duty finished asap, not staying behind to answer questions or leave commendations.
Of course, all mentors aren't like this. I'm only speaking from personal experience as a sprout.