Staying under water doesn't drown the player

Works for me. Are you in creative, perhaps?

no i was on hardcore mode in survival.

Still cannot reproduce. Please attach a video/screenshots of the issue and/or provide more detailed steps to reproduce.

i am making a video.

The video: https://www.youtube.com/watch?v=_riTCt569T0&feature=youtu.be

Does this happen every time? When it happens, can you mine blocks and drop/pick up items?

Yes I can mine and drop/pick up blocks.
In each world it wil happen.

Is this still an issue in 15w44b? If so, please explain the issue in detail and provide steps to reproduce it.

It works

Fixed somewhere between 15w44b and 15w37a.