Zombies on experimental appear to sustain aggro even when line of sight is broken several times. I've played around quite a bit, and there doesn't seem to be any way to get a zombie to stop chasing you. I've also had zombies become aggroed on me through walls and across extremely large distances. The zombies on stable also seem a bit too aggressive, but my sense is that the pathfinding improvements on experimental may have exacerbated the problem.