*Steps to Reproduce*
1. Use a structure block on a building made of cobblestone, mossy cobblestone, stone bricks, and stone. 

2. Use a repeat command block to spawn a lot of zombies. (/summon zombie x, y, z) The command block should be in the structure and the zombie spawning coordinates outside it.

3. Quickly destroy the command block and /kill @e.

4. Spawn zombies in the structure.

This should now hopefully recreate the bug. The world should be flat if that helps.

*Observed Results*
(MINECRAFT PE) Like a previous post I made, now Zombie Horses are spawning a couple of hundred blocks away from my main builds, and this time I didn't even do anything. To clarify last time I set a repeat command block to spawn zombies at a location and then when I destroyed the command block and killed the zombies I soon discovered that zombies were spawning repeatedly somewhere far away. I went on peaceful mode and tried a bunch of stuff. Then, I used a structure block to delete my castle where the repeat command block WAS placed and rebuilt it using the structure block and the bug fixed. This time I didn't even do anything except spawn 2 zombie horses and now there are so many zombie horses. If load the wrong chunk I get kicked out. Can't even use /kill @ e without getting kicked. Oh! And guess what? Zombie Horses don't die in Peaceful. I'm on a render distance of 4 right now, to stop the world from lagging. How do I kill all unloaded mobs and fix this? 

*Expected Results*
What should now be happening is nothing. No mobs should be spawning, my world shouldn't be crashing, I should be able to continue creating my adventure map without any troubles.

No pictures/videos because if I even try to load chunks with the zombie horses it kicks me out.