On PS you can rebuy when you drop below the max buy-in even if you still have live chips in the pot. It's a relatively easy way to quickly get a 200 or 300 BB stack (depending on whether or not your bet gets called, etc.).

A 1200 BB stack like this is another matter. This is pot limit so you can't get 1000BB in the pot very easily, and you still have to drop well below 100BB before you can re-buy. I wouldn't be surprised if as much as $6000 of that stack comes from this kind of trick, but most of it must be legitimate winnings.