When you use this game, you don't expect to always be in the middle of a block, so your position is stored using floating point variables. However, when the game is saved, your position seems to be stored as a set of 3 integers. This may be the cause for a lot of other bugs :
-Downwarp when reloading the world while falling : MCPE-10859.
-Downwarp when reloading the world while on the edge of a block : doesn't seem reported yet.
-Upwarp when reloading the world if not on a full block or falling in lava : MCPE-13213 and MCPE-10858.
-Mobs getting out of fenced areas when reloading : MCPE-1982.