Bad X-ray bug

Pushing a bottom half-slab into yourself using a piston while in crawl mode makes you able to look through blocks. This affects 1.14+, and 1.15 snapshots. I tested on singleplayer (all 1.15 snapshots, and all 1.14 releases), multiplayer (1.14, 1.14.2-1.14.4), and Spigot server (1.14-1.14.4). Tested in survival (multiplayer, spigot server, singleplayer) and creative (singleplayer only).