The market price used in Profit and Loss calculations is the composite of the pit and electronic sessions. This is useful for contracts that are fungible between pit and electronic and the pti and electronic sessions have different rading hours. Using the composite quote assures the profit/loss calculations use the most current quotes in the market.
"Orders & Positions" shows the Profit and Lost price as a single item under "net positions". This property allows traders who are using both pit and electronic markets to trade to view their positions in both markets combined into a singe "net" position, rather than viewing them separately.