I was playing the most recent snapshot: 13w21a, when I spotted the bug. I was flying around underwater when I spotted large pockets of air placed randomly underwater

I Was flying around underwater with night vision on when I saw pockets of air, about 3x5x7blocks and of varying sizes. They some appeared in clusters, or alone. You could swim inside and breathe air, as if it were a small, enclosed space, but there were no walls or anything. I was very confused, and I thought it best to file a report so the problem can be fixed before the next snapshot/ update. Thank you. -ShaboodleCrafter