Bunny causes NullPointerException

I was getting occasional crashes, like some have reported, till I started farming rabbits. I now get crashes all the time. I have about 150 rabbits in 16 x 16 fenced area aligned on chunk co-ordinates. The reports all show a NullPointerException on a bunny, different id's each time. I am usually not in sight of the bunnies, but the chunk is still loaded.