The bug:
You are able to suffocate in blocks when "sprint-swimming" in water. It's difficult to explain in words so please check out the attached screenshot and video*.

Reproduce:
1. Create the setup in the screenshot and video
2. Sprint-swim into the top of the bubble column (make sure you hold space the whole time)
3. Make sure you are still sprint-swimming and not standing up. Move forward while still holding space
→ You took damage but not from drowning (as you can't drown in bubble columns). The death message is "x suffocated in a wall" and not "x drowned".

Note:
Once you are Sprint-swimming, release the control key (if you had it held down) or you may not take damage.

*Unfortunately, the video is poor quality due to the 10MB limit.