If you are swimming underwater in Survival or adventure mode and you move up or down on the Y-Axis your air bubbles refill. Tested on multiple worlds too and i recorded some footage of it: http://www.youtube.com/watch?v=JeEWZ-k3KOc
Linked issues
Comments 2
Duplicate of MC-48395 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.
Confirmed