I've left mine in the USB slot on the back of my computer without problems.
The only problem I had was when I turned my computer into hibernation mode
then pulled the flash drive out, then turned on the computer, at which time
there was a tremendous amount of hard drive access for about 10 minutes
until I tried to shut it down at which time it sat at the shutting down
screen and I finally gave up waiting and just powered it off, when I turned
it back on it was back to normal.
But again, I've had no problem leaving the USB flash drive plugged into my
computer when I turn it *off*.