I know for sure I am not the only one having this problem but I am not finding much about it. Wolves are not spawning naturally on new maps (that is, created within the last 3 months or so) where we're using bukkit/spigot. They may not be spawning on old maps either, but previous spawns are still around of course. Worse, if you go into creative and spawn new wolves, even on old parts of maps, they almost immediately despawn. I have talked to server owners using spigot and I am using bukkit and this seems to be consistent across these two api's. The people I have talked to feel that this is in bukkit/spigot, since vanilla servers are working fine.