Swimming up water, even if you are where you would normally be able to swim up with water without losing air, causes you to lose air. This resulted in an unfortunate death on a server I was playing on. Further testing in survival proved it was not just a server glitch.
To reproduce this glitch:
Step 1: Swim on the edge of water where in previous versions you wouldn't drown. This is best reproduced on a waterfall.
Step 2: Start drowning
Step 3: Drown
Step 4: Despair