Waterlogging a block that can be moved by sticky pistons, then retracting the sticky piston vertically with the block attached, the water will disappear server-side but not client-side.
Steps to Reproduce
Place a slab
Place a sticky piston above and facing the slab with one block of separation between them
Waterlog the slab
Activate the sticky piston
Deactivate the sticky piston
Here, a single water source will appear under the slab. Reloading the chunk/ world makes it disappear. Items do not float and entities cannot drown in this space.
It also doesn't stop fall damage as normal water would do. Also, still affects 1.18.0.27