Nether mob drop rates

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