Breathing bubbles flickering if in air pocket underwater

While swimming in a river I used a bucket to create a stable 1x1x1 air pocket_{Picture 1} (probably another bug) underwater. I tried to refill my air by putting my head into the pocket.

What I expected to happen:
My breath slowly refilling, bubbles going to maximum.

What actually happened:
The air bubbles flickered around, then they get removed (as if you were submerged in water). After a short amount of time I drowned.

How to reproduce:
1. Go to a river/ocean
2. Set your gamemode to survival (not creative)
3. Create a stable 1x1x1 air pocket underwater two blocks above the river/ocean floor like in Picture 1.

How to make the air pocket: (Gif)

• Take a bucket

• Hold down right-click (use bucket) and move your mouse up and down fast (as I do in the gif)

• the bucket takes water and gets emptied immediatly, then the watersource that would flow into the air space gets taken up again --> no new blockupdate

4. Stand in it pay attention: your head must be in the air pocket and watch how you drown. (video)