The jerking is normal in my experience. There's always some slack in the primary chain, geartrain, sprocket spline, and final drive chain. At low RPM the engine doesn't turn smoothly like an electric motor: the crank jerks "forward" with each power stroke and slows down considerably between them. The rear wheel and all the slack in the drive will jerk around oscillating in response to the engine's erratic instantaneous RPM. You can probably find a low RPM that excites this oscillation best, causing a dramatic wheel jerking and chain slapping.
At higher revs this crank speedup/slowdown alternation happens at a frequency above resonance in the wheel/drivetrain system.
With the wheel on the ground its motion is limited to whatever rotation speed it has, it can't jerk around freely. If you look at a lot of bikes on tghe highway you'll see a few where the chain is whipping pretty wildly although the bike is cruising at constant speed - the chain's resonant frequency happens to be the same as the engine's power pulses. Big singles and V-twins do this more than fours or smaller displacement bikes where the cruising RPM is well above the resonance area.
