On the multiplayer server i play most often both tamed ocelots, and to a lesser extent tamed wolves will randomly despawn if left in a chunk when it is no longer loaded on any players game. A lot of the players have the despawn issue with the tamed ocelots, they even despawn if tied to a fencepost with a lead. A much smaller number of players have this same issue with wolves. For example i have the issue with the ocelots but not the wolves, other players have it solely with the wolves, it seems almost individual. I know it isnt a matter of animals per area/chunk, some have had their animals disappear when it was the only one they had.