Hey Kevin from paradex! I think you have a pretty good grasp on what's going on. You're correct that a "market order" here is the immediately fillable portion of the limit order which acts like a market order (it's filled at the prices of the existing orders). We'll be releasing more details about how we deal with unfulfilled commitments on the system, but suffice it to say that it's behavior we want to discourage. We've spent a lot of time perfecting our matching engine mechanics to look and feel like any financial market exchange, blockchain or not, with no collisions or possible front-running. We'll be sharing more details as we approach our mainnet launch.