In the seed 6627885220816235195, when I spawn trees start turning into dirt. My friend and I both checked this on other computers, and it came up with the same outcome. Also, my friend said that is was only this seed.

Anyway, so what happened is that the trees in a certain area slowly started to turn to dirt. You could see it in front of your eyes. (158, y, 148)

Also, nearby you could see trees catch fire when there was no notable lava nearby. (239, y, 235)