I've used a USB Stick a number of times and never had this problem.
In any # Linux Distros including Mandriva, and whenever I'd plug in my stick, it would show up, then once I removed it it would disapear....
Just a hunch even though you don't have one plugged in, Check your Bios to see if it maybe config in your bootup ie: HDD1 CD/DVD Floppy etc.
Even if you haven't got a USB set in your boot up, try Flashing your Bios and reset everything.
And see if that works...
Like I said just a hunch but it might just work.
It's worth the shot.