Blaze's fireballs don't light fire

THIS WORKS ON ALL OTHER WORLDS I HAVE GENERATED

In a specific world blaze's fireballs don't set blocks on fire when they land. The biome was 'MushroomIsland' and the coordinates were x=290 z=-540

I can't explain why it works on other worlds but not this one...

I couldn't attach the world file, so here's a download link: https://docs.google.com/uc?export=download&id=0B91NRh_gXbmMYUVFQWpLMDNTZVU