I'm afraid this issue is occurring more often with the new P-3 model, than with it's predecessors P2-V and V+. I flown those models quite a bit over water with no issues for over a yr. now. The battery fit on those models was much different than on the new P-3, requiring quite a bit of strength to simply remove the battery from its holder. The P-3 doesn't appear to fit as snug, and requires less manipulation to remove the battery. The pendulum has swung to the other side, so to speak, and now there may be more concern of the battery dislodging for one reason or the another. On the other side of the coin, there very well may be the possibility of defective batteries making there way to prospective P-3 customers which can not be ruled out, until proven otherwise.
I honestly believe this incident as disheartening as it is, has nothing to do with the model being flown over water.
I do agree, although DJI for what ever reason now recommends not flying over water, has done quite a bit of advertising showing same, and believe if they feel the model should not be flown over water should place a disclaimer warning not to be flown in that manner when advertising the Phantom, IMO.