The bug

Based on MC-1788 ocelots should not spawn if Peaceful is set as difficulty. However when reopening a world with Peaceful as difficulty they will spawn.

How to reproduce

1. Create a Superflat world with the following preset

   3;minecraft:grass;21;
   

2. Set the difficulty to Peaceful
3. Kill all other currently existing entities

   /kill @e[type=!player]
   

4. Wait some time
   → You should not see any ocelots spawning
5. Reopen the world
   → Ocelots start spawning despite the fact that the difficulty is still Peaceful