Fire no longer either spreads, destroys flammable blocks nor gets extinguished by rain.

Fire doesn't spread, consume flammable blocks nor disappear with rain anymore. Perhaps this issue also happens with water being unable to extinguish fire. This is most easily seen in the Overworld, which is perhaps one of the reasons because of which this bug has remained unnoticed, since this beta is mostly centered around the Nether as we all know.