Affects Version/s: Minecraft 18w15a, Minecraft 18w16a
Fix Version/s: Minecraft 18w19a
Found some kelp that spawned on the trapdoor on a sunken ship. The issue is when you open the trapdoor it stays floating in the water above it.
Coordinates: /tp -407 50 2254 (for stairs and trapdoors)
Coordinates: /tp 514 56 1536 (for chest and slabs)