Is anybody else noticing this seemingly new behaviour in 1.0? Zombie jumps a gap, then immediately moves to the side to allow another zombie to jump there.
In these 2 pics, the ledge is only 1 block wide. He moves to the edge so that another zombie can jump there. It also prevents you from hitting him since you can't attack through the smaller slit (melee at least). It forces you to go forward to attack through the centre gap. Then of course, he cheap shots ya.