A few zombies killed me near spawn point so I quickly respawned returned to the place but didn't see my items. I also heard but could not see the zombies. I wandered around a bit and started picking up my items despite not seeing them. I also got attacked by the now invisible zombies, fought back and killed one (the rotten flesh drop of which was visible), but continued to not see them. Then the sun came up and I heard them getting hurt in the sunlight but saw no fire or the zombies themselves. I'm not sure if this glitch was just a display error or a bug within 15w38a - but it sure was one of the more bizarre mishaps I've encountered in the game.