This problem has very specific steps to replicate it. It only happens in multiplayer games, but I have only tried it with two players on the same system at the same time. If the host changes game mode from survival to creative there are no issues. If the secondary person changes their personal game mode to creative, the problem starts. When the secondary person hits 'x' twice to fly, suddenly they start taking on damage until eventually they die and the message says "player has fallen from a high place".

Obviously with no hearts you shouldn't be able to die, nor does the person fall while they are flying in creative mode.