Active effects doesn't really work that great.

What I expected to happen was a creeper with a working speed effect.
I put in this command:

/summon Creeper ~ ~ ~ {ActiveEffects:[{Id:1,Amplifier:50,Duration:999999}]}

What actually happened was that I got a creeper with particles of speed, but the effect didn't really work. But when I gave it another effect with a splash potion, the speed effect did work.

Steps to Reproduce:
1. do this command:

/summon Creeper ~ ~ ~ {ActiveEffects:[{Id:1,Amplifier:50,Duration:999999}]}

2. See that it doesn't work.

3. Splash it with a speed splash potion.