Is this a problem for anyone with money in MTGox? i.e. would sales inside MTGox have counted towards this tax or isn't only with withdrawl/deposit into their e

Is this a problem for anyone with money in MTGox? i.e. would sales inside MTGox have counted towards this tax or isn't only with withdrawl/deposit into their ecosystem. I can imagine that if internal to MTGox interactions are treated this way then there are a lot of people who sustained a capital loss higher than that and had no option to withdrawl the money to pay taxes.