Drop rates for some nether mobs is wrong.  Blazes are dripping at least 1, and often multiple, blaze rods per kill without looting.  Average seems to be 2 each.  Wither skeleton heads drop around 25% of the time, about ten times more often than they should.  5 heads in less than 20 kills.  Both blaze and wither skeleton were killed using a bow, so there definitely should not be a looting type effect