okay so, I am not certain if this is a complete bug, but I have noticed it for a while and am starting to think it may BE a bug. so, normally I can find a minecraft jungle and there's a good chance for ocelots right? well, I started playing minecraft while it was in 1.6.4 and lived in a desert with some nice space, and eventually found a jungle. I found some ocelots, but obviously I was clueless how to tame them, so I looked it up and planned to come back. however, from the point I found the jungle I switched the difficulty to easy and back to peaceful after a while. when I returned to the tiny jungle, there were no ocelots at all. so at first I thought it might have had them despawn so I haven't been back to that jungle in quite a while. but recently, while playing new versions of minecraft, I have found that:

if I change the difficulty when not in a jungle after finding and entering one,
when I return to that jungle, ocelots disappear. and I don't mean they become scarce, its like they all disappear and they DONT respawn. ever. and my current issue right now DID start while using mods, but I have had these issues even before I knew what a mod was. so basic break down:

1. Pick a seed, have the difficulty to what you like.

2. look for a jungle explore it a little, and then leave at least 70 blocks away.

3. change your difficulty to something different, I've found peaceful from difficulty mode is where mine occurs typically.

after having it on that mode for at least 2 minecraft days, return to the jungle.

5. by then, the ocelots typically despawn for me.

P.s. I am not certain if its just me, or if this really is an actual bug, but it has happened from 1.6.4 to 1.8.9 with and without mods. and the only reasons I have yet to experience on 1.9 or 1.10 is that I have not found a jungle for those versions. and it tells me I HAVE to label that version alone, but I am more or less trying to make it aware so we can make certain that isn't in later versions.