Me and my brother are swimming across the ocean. We came across an unloaded chunk, but since we were in the ocean, we figured we wouldn't come across anything too deadly. Suddenly, I see the death message "[brother] fell from a high place". Sure enough, he had died of fall damage... in the middle of the ocean! His items floated to the invisible surface of the water, proving that there was, in fact, water there. (Note that I did not, and he was directly following me.) This wasn't the first time it had happened; it happened back a while ago as well. 

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