I wanted to check out the new lush caves. I got a little bored by the generation, as I had spawned in a bad area (not a bug, just uninteresting) and decided to build a house with a copper roof, as I hadn't played too much with the previous snapshots. I built the roof out of cut copper stairs, and while I was decorating the house, I turned the randomTickSpeed gamerule up to 100,000. High numbers like that are often buggy, so I was expecting something to happen. I noticed that some of the logs and planks I was building with were being replaced by stairs as the nearby stairs weathered. The block space that contained the affected log did once contain a cut copper stair block. I replaced it with the log, but then, the log was replaced with a lightly weathered cut copper stair block. Later, some of the wooden planks were moved a block away from their original positions. I forget whether they also replaced cut copper stairs.