This is a bug thats been in mcpe since 1.0 released however i havent been able to get proof of the existence of this bug till recently, below is a video where i walk, and boat through a realm until i get trolled by my kindle saying im running out of space but it then turning out the video is only 36mb and i still have 50% memory left

https://youtu.be/sO1pwY-7pe0