I am playing on peaceful in a tower without any entities (items, mobs, animals, item frames, etc). I am surrounded by Stone Bricks, and Regular Glass Blocks, Wool, and Jungle Planks, Slabs, and Stairs , and the co-ordinates specified is on top of a 2x2 white wool surrounded by orange wool. And not that it matters, but the only things in this large room is a chandelier made of Iron Bars, Oak Fence, and Torches

My redstone setup is a leaver on a testfor command block which leads through a comparator into a lamp. Very simple setup.

testfor @e[x=-84,y=144,z=177]
testfor @e[-84,144,177]
The return of both of these commands returns more information then my chat can hold, but what is in my chat is:
[@: Found Zombie]
[@: Found Squid]
[@: Found Pig]
[@: Found Zombie]
[@: Found Squid]
[@: Found Pig]
[@: Found Squid]
[@: Found Zombie]
[@: Found Pig]
[@: Found Squid]
[@: Found Bat]
[@: Found Pig]
[@: Found Zombie]
[@: Found Witch]
[@: Found Squid]
[@: Found Spider]
[@: Found Pig]
[@: Found Pig]
[@: Found Spider]
[@: Found Skeleton]
[@: Found Sheep]
[@: Found Pig]x3
[@: Found Creeper]x3
[@: Found Pig]
[@: Found Creeper]
[@: Found Pig]
[@: Found Creeper]
[@: Found Creeper]
[@: Found Sheep]
[@: Found Pig]x3
[@: Found Sheep]
... and so on. Remember, I'm playing on peaceful at the top of a tower with no entities within at least 50 blocks.

And to better test this bug:
testfor @e[type=Creeper,x=-84,y=144,z=177]

• returns 14 Creepers, even though I'm not only on Peaceful, but I'm only testing one point with no range

I also tested the same Creeper testfor with different range values and returned different results. 0-148 returns 0 Creepers. 149 returns 3 Creepers. 150+ returns more and more. However, 150 seems to go back and forth between 3 and 4. This makes me think that where ever these entities are, they're moving?