i was just familiarizing myself with the new Bendy Bones to plan a rig when i ran into this problem. ...gif below. it's unlikely that i caused it, cuz what you see is a really simple setup and the problem persisted every time i recreated the setup: add a bendy bone, add a mesh, weight. it's disappointing - i could really use that property.
edit: what i mean is that it's not affecting the mesh like Curve XY Offsets or Scale :]
however, you can see on this youtube video: https://www.youtube.com/watch?v=nQCo2AGRT6o, it actually works as it's supposed to. he's using 2.77.1 and i'm using 2.78.