Before I got 13w25b on the new launcher, I was playing 13w24a, so I'm not quite sure if it is a problem with 13w25a. When I logged into my server all my wolves had really low health. I figured someone hurt them, so I healed them. I got off, and then got on a while later and their health was down again. I checked my server logs, and nobody was on between the time I got off and got on. It looks like their health was as low as a wild wolf, judging by their tail. Im not sure if this happens in singleplayer.