Comparators not comparing

Whenever a comparator is "receiving" from a command block that has the command "testfor" in it and the output is greater than 15, the comparator "ignores" any side input.

Steps to reproduce:
1. Get a command block with this command: testfor @e.
2. Have a comparator coming out of the command block.
3. Add redstone and redstone repeaters to make a comparator clock.
4. Spawn more than 15 mobs.

Extra Info: I was on snapshot 14w07a. I don't know if it is a bug on earlier snapshots.