Mobs that burn in sunlight catch fire when overcast in rainless biomes

In dry biomes such as the desert, mobs that burn in the sunlight will catch on fire even if it is overcast (when it would be raining or snowing in a different biome. Sometimes the fire stops, then starts up again shortly after.

1. Enter a dry biome such as a desert
2. type /weather rain
3. Spawn a zombie, skeleton etc.