The Ninth is cheeky. Prokofiev could be cheeky, too, but there's more often a straightforwardness to his humor that's alien to Shostakovich. Even Sh's early works are closer to cheeky than just plain fun. I think it's as much a personality difference as anything. I get the impression that Prokofiev was merely bewildered by the Zhdanov decrees; Shostakovich had been through it all before.