(First, I want to say sorry for typing a bug for MCPE in the MCPC slot)
This happened on several worlds ever since the 0.9.0 alpha update. What basically happens is that when you die or are killed, 80% of the time, you would glitch through the 'floor' of the world and would fall while suffocating in bedrock and/or burning in lava. (This happens to the host of the world also)
It's very inconvenient and quite odd. It also happens on old minecraft worlds and infinate worlds. Although, glitching through lava seems to happen more often on old minecraft worlds. When respawning on old minecraft worlds, you would glitch through the void, saying this, you would technically be able to 'fly' through the void. Hope you know what has happened.