Affects Version/s: Minecraft 18w31a
Fix Version/s: None
OS: Windows 10 Pro
CPU: Intel i5-7500
GPU: GTX 980Ti
The discovery: While removing a mass amount of sand with an Efficiency 4 diamond shovel in a survival world, sand landed on top of my character and I began to suffocate, moments later I began to fall through the world underneath the bedrock layer.
Note: While suffocating, you can see all the blocks you fall through as you continue going downwards at an increasing speed. You will stop falling through blocks once you stand inside an air block.
Only one falling block is required.
Does not work with Anvils, only full blocks seem to cause this (sand, red sand, gravel, concrete powder, etc.)
Test: (see attachments)