Plugging an USB disk fucks MBR!?

This will sound strange, and I didn't believe it myself, but I've verified for three times that in this machine running Windows XP SP4, the MBR or boot sector gets corrupted by plugging an USB disk — three different devices I tried (one flash disk, two hard disks). Every time I plug something, something manages to fuck with the MBR or boot sector and from next boot I can't boot Windows. Did this illogical thing happen to any of you?

Also, any ways to restore a Windows MBR or boot sector? FIXMBR and FIXBOOT didn't work, as usual.

Take some XTC laced with PCP and a bit of LSD, then turn on your PC, plug the USB into the CPU, put in a CD with some CCR, then hit up the WWW, but stay away from the CP unless you want to deal with the FBI.