It could be due to the camera's "steady shot" technology (whatever Canon calls it -- that's Sony's term, I think). Probably all cameras today have some form of image stabilization, designed to reduce the shakiness of handheld shots.

Most consumer cameras have electronic image stabilization. In simple terms, the camera captures a bigger image than what you see on your LCD screen, and then it moves a little "crop" window around inside that larger image trying to stay locked in on your main subject. If you move your camera a little to the right, it moves its crop window to the left, trying to hold onto the original part of the image -- the part that was in the center of your image before you started moving to the right.

Are you shooting with a tripod? These image stabilization features are tremendously beneficial for hand-held shots, but work against you on tripod shots. For tripod shots, learn how to disable the stabilization feature.

If you have the camera on a tripod, and have the image stabilization engaged, you might notice a lag when you start to pan. For example, you start panning to the right, but your image looks like it doesn't move for the first second or so. What has happened is that as you started to pan to the right, the stabilization feature tried to stay locked on your original image. The camera doesn't know that this motion is intentional. It's little crop window eventually ended up all the way to the left of the sensor, and at that point it had no choice but to now show the actual panning motion.

Once you stopped panning, the stabilization feature tries to ease itself back to the center of the sensor image, so you've stopped your pan motion, but the camera's image continues moving a little bit more to center itself up again.

Even if you are not using a tripod and notice this behavior, it might be the image stabilization that is causing the lingering motion you observe.