Flying with the elytra, when you look up and fall whilst flight is engaged, you fall through the floor bellow into the void. In creative you can fly back up through the floor and in both survival and creative, you cannot move out of the position you are in (x and z coords). You cannot teleport out of this position and when teleporting to yourself, the coords change to NaN, ycoord, NaN. In suspended flight the legs and arms appear missing.