Switch off PSC 2175 and it powers down the PC too.

This is a strange one. When I power off my PSC 2175 it seems to cut power to my Praesario desktop forcing the PC to reboot. The printer is connected via USB 2.0 and I have just installed the most up to date Drivers (that's not the cause as it has happened previously). The PC is running XP Home, SP3, Pentium D 3.20 Ghz.