That does not work. Legally they can't take those Bitcoins from you. You would have to have bought them knowingly in order for them to charge them back to themself. Everything else is theft on their side.
What they could do is raise the fees to trade and withdraw in order to get their lost bitcoin back.
I think this thread proves that Gox does not care what they can legally do. Good luck claiming theft when they decide to charge your coins back.