Correct, a low oil level in the damper will cause a lean condition on acceleration/goosing the throttle. The piston is able to rise too fast, causing more air than fuel to be drawn into the intake. Your air/fuel ratio should smooth out once you are going down the road at a stable cruising speed. Anymore than a cruising speed, and you may cause the pistons to sort of vibrate up and down quickly, which will give a messed up air/fuel ratio, too.
Oh, and I've never had the oil in the piston damper go anywhere without the cap on. It just sort of sits there.