When you kill invisible horse variants, the screen will turn red/black

saw this in sethbling's livestream on the 17.02.14
How to reproduce:

• there has to be another horse entity before spawning the variant 7 fienxjox
• summon a invisible horse variant (/summon EntityHorse ~ ~ ~ {Variant:7}

  )

• kill the horse (/kill @e[type=EntityHorse])
• the invisible horse has to be the last spawned entity