Mode: Creative (haven't tested sruvival, could be there too). Reproduce: simply enter a game, find a build, select a block, pres pg up/down on your keyboard, and the block will be placed above/below where it was previewed. Description: This is a bug I've noticed in Creative. I have made a video (below) showcasing the bug, since it's easier to show than to try and describe it. Please let me know if more info is needed.