Summary:

Several problems happen when trying to build at a high y-level, including suffocation, blocks failing to be placed, and sometimes falling through the block currently standing after leaving and re-entering the world

Step to reproduce:

1. Create a new flat world
2. Spawn a block at y-level higher or equal to 255
3. Give yourself some blocks
4. Start placing to extend the platform
5. After abnormalities happen, leave and re-enter the world

Expected result:

Blocks should be placed normally

Observed result:

Sometimes we'll take suffocate damage, blocks often fail to be placed and several attempts are required. Leaving and re-entering the world sometimes result in falling straight down through the block that player was standing before leaving the world.