You may never know, lol, but...
When you buy any peace of hardware, it is always useful to install drivers
for the device from the manufacturer's disk that came with the package, or a newer setup version downloaded from the manufacturer's website online; even though you may not need the actual software that supports the drivers, it always does help when using the hardware in general. This goes for mice and keyboards as much as any other peace of hardware (like GPU and sound).
So if you continue experiencing these issues, try and install the drivers for the mouse (unless its a totally generic PS2/USB device).