In some trackballs and spinners, if you spin them too fast, they will not work correctly. There are many threads on BYOAC.com discussing a phenomenon where the device will move opposite to what you specified if moved too quickly. These problems are caused by the poling rate of the device and the rate at which you spin the encoder disk. I'm not going to get too technical here, but when you move the trackball, you spin little shafts underneath it. Those shafts have encoder wheels (like little pinwheels) attached to them at one end. Those encoders sit in-between a LED emitter and LED detector (sometimes a single unit, sometimes two components). When you spin the ball/spinner, the encoder disk spins and breaks the light beam. Depending on the direction of spin, the device will respond according to what you input. Now the problem comes in when you consider that the device only checks the light beam every so many milliseconds. If you spin the wheel fast enough that the light beam is broken and then unbroken before the device poles again, it won't know that you moved anything. If you slow down slightly, it will catch the tail end of the beam being unbroken and think you are moving backwards or maybe just twitching it. If you slow down even more, it will then see what's going on correctly and the cursor will shoot across the screen. Something else COULD be going on, but this is the most likely cause. The solution many people have looked at is using a program to increase the poling rate of their PS/2 interface devices (mouse hack), or moving to USB.