Unexpected Results "/spreadplayers" MCWin10 v1.2.8

I'm having unexpected results when using the "/spreadplayers" command on Minecraft : Windows 10 Edition v 1.2.8

What I expect to happen...

Have hostile mobs, example "Creepers", spread around the play area, which is 128 x 128 block area.

The command I'm using:

/spreadplayers 64 64 5 64 @e[type=creeper]

What actually happens....

Mobs although they do spread out in a random area within the set x and z axis, they're also teleporting into the air along the y axis, and falling to their deaths.

Steps to Reproduce:

1. Create New World :

Game Mode Creative
Difficulty: Normal
World Type: Flat
Mob Spawning: False

2. Teleport to 64 4 64

3. Spawn 24 Creepers

4. Attempt to spread spawned creepers with:

/spreadplayers 64 64 5 64 @e[type=creeper]

5. Results Creepers falling to their deaths spread across the specified x and z coordinates.