Just acquired a used AF100 and Lumix G Vario 14-140 Lens. I'm getting a strange back-and-forth "shuddering/warping" in my video frame when there's any movement in the shot and the camera is set to Auto Focus. It's as though the camera is shaking or vibrating slightly (which it isn't, being that it's on a tripod). The problem disappears as soon as I switch to Manual Focus. (Also tried OIS on and off, with no effect on the problem.)

Here's a link to a brief video sample: wobble sample - YouTube (http://youtu.be/33uQ2cwpb9E)

I'd appreciate any insights into this?

Looks like lens breathing when focus changes changing the size of the frame at different focal lengths in time to your movements.

Thanks Daniel. Is this "lens breathing" normal for Auto Focus ... or is it a problem with the camera or lens? If it's normal, is there any camera setting that would minimize this effect?

Lens Breathing is typically more noticeable on zoom lenses when changing focus. It can also be seen on prime lenses that are not designed to minimize it. If you want to see it using manual focus you should change the focus back and forth like Auto focus might do as in your sample. You should see the frame size change. This is why video lenses aren't as good for rack focus shots if you mind the size change. Cine style lenses often are designed to avoid or minimize this.