Dissemination of material news that can affect a stock's price is not limited to regular trading hours (RTH). Markets are moved in the after or pre-market sessions by traders seeking to react quickly to the initial dissemination of positive or negative news. To address price movements outside of the Regular Trading Hours session, Interactive Brokers will simulate a price movement on derivatives (which only trade during RTH) while tracking the underlying (which continues to trade outside of RTH). This is designed to value your portfolio using two different mark prices, Real and Forecasted, which will provide account holders with a more accurate view of their Net Liquidation Value and one of the two possible outcomes listed below:
1) Accounts may experience a positive adjustment of Net Liquidation Uncertainty, which could prevent liquidations of other positions that are actively traded outside of RTH, or
2) Accounts could experience a negative adjustment of Net Liquidations Uncertainty, which will prevent accounts from entering new orders that could not be supported when the markets re-open and the forecast mark prices are replaced with the prevailing market prices.