It seems I’ve run into a problem with the 100–400mm lens that I purchased this past June. The image in the viewfinder began jumping around when I pressed the shutter button half-way—often this would continue even after shutter release. I contacted Canon’s customer service. Based on my description of the problem they suspected the image stabilization had failed. I sent the lens to their service center and they accepted the lens under warranty. I hope to have it back in about another week. I’ll let you know how the process went, as well as how the lens works when I get it back into the field.
