I think my dog has done it. . . . . twice.
Both times, it was a squatter in long ish grass, and he trotted down the beam slow and as he got near, kind of accelerated and jumped at the same time, I suppose a pounce, and both times, nailed the bunny in the seat.
Every other time, its flat out down the beam, and i've seen him catch rabbits sat very close to the fence, and on occasion just inside the fence / hedge, by suddenly coming at them like a small, black, bat out of hell, and panicking them into doing something stupid, or just nailing them before they can think / act.