A6000 video jitter

While using my A6000 to film a skiing event I found that a large number of shots were unuseable due to jitter. Panning - no problem, tilting - no problem but holding a fixed frame and allowing a skier to whizz past camera, the skier jittered badly. If the subject was fairly distant, the effect was a little less noticeable. Record setting: 1440x1080  12m.  File format: MP4. Steadyshot: on. As the A6000 is basically a still camera, was the steadyshot trying to "grab" images? I am editing on FCP7 with a new video board in my MacPro. In any case the jitter is evident when simply viewing the rushes with Quicktime Player 10.4 or MPEG streamclip. In previous years I have used my trusty Sony V1E (DV CAM) which copes with all the action I can throw at it!  Any thoughts would be very much appreciated.