The bug

When an item has floated to the top of a block of water it is inside of and is below an opaque block, the animation of it bobbing up and down can cause it to visually disappear into the block above it.

How to reproduce

1. Have a region of water which is below an opaque block
2. Drop an item inside the water
3. Observe

Expected results

The item would always be visible.

Actual results

The item's moving-up-and-down animation causes it to periodically phase into the block above it and become impossible to see for a moment.

How to fix

It may be worth removing the moving-up-and-down animation for items which are submerged in water, and only have it play when they reach the surface. The same could be doen for other blocks such as cobwebs, fixing MC-199964.