If I use 'Quit to Title', and then re-enter my world, I get spawned on top of the highest block over my head.
This is a problem, if I'm mining deep under a mountain, and I happen to re-enter the world at night time, I am now on top of the mountain, and need to fight my way to the base through the monsters that are spawning, to get back to where I left the game.
Even worse, I was mining underwater (as in, my tunnel was under ground under the water), and I spawned above the water in the middle of the night. I didn't realize what was happening until I was drowning.
If you did not already, please remember to perform a search before creating a ticket to see if your bug hasn't already been reported. This issue was reported previously as MCPE-7037. Comment your experience there!