At some points you'll start seeing multiple mouses. Partly because OSes are pretty terrible at displaying mouse cursors (I guess).
Umm.. are you sure it is OS problem? I think it is because of how human eyes work. Their refresh rate is lower than the speed you are moving mouse, that's why you start seeing "ghost" mouse cursors.
I think if you'll record screen capture, and play back slowly, you'll see only one mouse cursor at any time (if screen is captured perfectly).