After changing the NoAI tag of Mobs, mobs will suddenly be hurled into the sky very high.
Steps to Reproduce:
1. Make a large-enough lake or find one
2. Put any Mob in the water
3. Run command:
/entitydata @e {NoAI:1}4. Wait 2-3 seconds
5. Run command:
/entitydata @e {NoAI:0}Repeat(if not reproduced)
Confirmed, it seems that the cause is that NoAI Mobs still try to "swim" and NoAI Mobs store Velocity. I stood in the same space as the Zombie and it flew horizontally when NoAI was 0 again.