[Jeremy Cox]

Make sure your Shutter Phase is set to 0 and that none of your keyframes are between frames (can happen if you are stretching or time remapping). After effects thinks the motion is starting/stopping part way through the frame. Imagine if you took a photo with the shutter speed set to 1 second, but the camera was moving for the first 1/2 second and was perfectly still for the second 1/2 second.