Remember man... going from SD DVX to full hd 1920 HD, and the camera is so tiny, you see every little jerk. You need some form of stable shooting.
Actually I experienced the same thing - a wierd jerk in the video. Only difference form the OP was that my Gh1 was mounted on a Manfrotto 503 tripod, and that I was using the 14-140 lens. The footage did a quick jerk vertically twice, while I was doing a slow pan to the right, with the lens at max tele.
I DO suspect that it was the stabilizer - maybe it was looking for something to stabilize? That happened to be my first shoot with the GH1 - has never happened again. But nowadays i keep the stabilizer off when mounted on a tripod.