Camera face tracking?

I noticed a odd thing today regarding the camera on the N95. I had the phone stood upright on a windowsill whilst i stood a meter or so away and recorded a video of myself. When i played back the film i saw quite noticable that the camera image seemed to shift with my movements. Not by a massive amount, but enough to ensure that my face stayed in the shot if i moved slightly out of the centre of the image. Their was nothing else moving in the background and the windowsill is pretty solid so i find it unlikely it was the actually phone moving due to vibrations. So.....has anyone else noticed this? Any ideas?