In Multiplayer, if you have tamed a wolf, and either you punch another player or another player punches you, your wolf (or wolves) will start growling, but still looks the same. Also, it won't hunt down the player they are aggressive against. It is then possible for them to despawn. I have found no way to fix this. Making the wolf sit down does not change anything. last tested after 1.4, does not seem to happen in LAN multiplayer.