Holding space bar and the sneak button normally keeps a player in mid air when done in creative. This is used to place in blocks like hoppers without touching the ground.
This stalling in mid air will abruptly stop working when working under water.
- Be in Creative mode
- Go under water
- Make sure you are in creative flying mode
- Press shift (sneak)
- Then, press space bar (jump) and continue to hold shift (sneak)
- Wait about 2 seconds
→ The player will all of a sudden start sneaking and sinks to the ground, without any user input