It happens all the time, David. The casino doesn't net your wins/losses when determining when it has to issue a tax statement. If you win the US$1200 on a single spin, you get the W-2. It's up to you to keep track of losses and net them when doing your annual US federal tax return.

With the new voucher machines, you will get a hand pay of the jackpot amount along with the tax document and your credits from previous play stay on the machine. At least it's worked that way where ever I've played in Nevada.