Summary:

If a block is placed next to or above a waterlogged block, or a bucket is used to change the waterlogged state of a block (placing or removing water), then a ghost version of the base block appears client-side. This causes many errors (incomplete list):

• For beds and double chests, this only occurs when one half of the block is waterlogged.
• If the entire bed and double chest are waterlogged, the blocks themselves stop rendering instead.
• When water disappears on affected blocks, entering the space plays the water splashing sound once instead of twice (unintended, yet useful: MCPE-126671).
• When water disappears on affected blocks, entering the space allows the client to move at full walking speed.
• Trying to break an affected block will fail once, even in creative mode (in survival mode, the breaking textures appear, but resets once).
• Using a sticky piston to retract an affected block moves the server-side block, but also keeps the client-side ghost block in the original space.
• If the base (not head) of an extended sticky piston is affected, then placing a movable block on the piston head, attempting to break the piston base once, and deactivating the piston, causes the client to crash.

Steps to Reproduce (When using a water bucket):

1. Dig a 1 block deep hole
2. Place a waterloggable block in the hole
3. Waterlog the block
4. Dig a 2 block wide, 1 block deep hole
5. Place a bed or double chest in the hole
6. Waterlog the bed or double chest

Observed Results:
At step 3, the water renders for a split second and then stops rendering.
At step 6, the bed and double chest stop rendering.

Expected Results:
The water, bed, and double chest should all render correctly.

Steps to Reproduce (When placing blocks):

1. Navigate to a flat area
2. Break one block in the ground
3. Place water in the space
4. Place a waterloggable block in the space (lever, stair, sign, slab, ladder, carpet, or another if desired)
5. Place any block above or horizontally adjacent to the space

Observed Results:
The water disappears.

Expected Results:
The block appears submerged in a water source.

Video:

Minecraft 2021-07-23 13-53-44.mp4
Minecraft 2021-07-23 13-54-13.mp4
https://youtu.be/5EpK6FiLSo8
Keywords for search: disappear invisible show appear