This is noticeable with image stabilisation turned on. It can be avoided by turning off IS, however if you do that you will obviously encounter normal stabilisation issues. I also find it a little annoying at times, but generally the image stabilisation tends to work fairly well. Sorry I don't have a good fix! I would just suggest trying to keep the camera as stable as possible, even when IS is turned on. Also, turning guidelines on helps me ensure that I keep the horizon or other objects fixed in the frame when I'm filming - it's helped me avoid this problem with some of my footage.