Interesting. Maybe that is what Thom Hogan was talking about:
"Are there times when it shifts where it imparts a change to the image quality other than pure stabilization? I believe there are, though the impact is visually subtle. Some of the mid-range distance bokeh of certain VR lenses appears to be impacted by VR being on. Put another way, the background in the scene is slightly moving differently than the focus point in the optical path. This results in what I call "busy bokeh," or bokeh that doesn't have that simple shape and regularity we expect out of the highest quality glass."