Hi marciton,
Some AV’s (like MacAfee, and now avast apparently), think it could be virus because it uses handles and hooks in order to close applications running on your usb, and then eject it. That is why it is flagged.
At their blog (appaholic.co.uk) it is stated that the application/tool is not a virus, so it may well be a false positive, detected by avast's heuristics.
If you have any doubts, try using virustotal.com
you can upload any file there and it tests it against various av scanners at once.
Please post the virustotal results here in your next posting,
polonus