What causes an erratic mouse in the shut down window?

If I choose Shut Down from the start menu, a window appears with shut
down selected and then gradually the background of the screen goes dark.
This part is normal. However, also during this time, the mouse becomes
jumpy and uncontrollable.

I am using Windows Server 2003 standard edition (32-bit). And it's
running on an Arima HDAMA board with dual 248 Opterons and 2 GB RAM
using default BIOS settings.

I have tried this on two Dells both running W2K3 standard, and I don't
see this behavior, so the question is whether it's Opteron/motherboard
specific or it just shouldn't happen at all. I don't generally see this
behavior anywhere else in this Windows, but it is easy to make it happen
just by copying files using the 64-bit preview edition of W2K3 on this
computer. In that case, all mouse control is eventually lost and the
computer must be rebooted.