I wonder if this is similar to what I'm experiencing? I wouldn't exactly call mine "bucking and jerking"; close, but it's much more subtle:
If I ride on a level, or slight downhill, and hold the throttle to keep a constant speed where the engine isn't really pushing the bike, but just keeping up with it, it feels like it's cycling between power and none, almost as if I was rolling on and off the throttle, even though I'm not.
I wonder if some EFI or sensor deal is automatically adjusting the fuel - too much, then not enough, then back to too much. It isn't too often that I find myself riding in this state; usually the engine is either pushing or braking, but when I hit that "coasting" sweet spot it likes to push me around a bit...