Quote from rationalmind:
IB is the only broker that I'm aware of that autoliquidates within minutes (most brokers give you at least a day, and more importantly, calulate your margin based on closing prices). Most people know that, but what they don't know is that IB recomputes your portfolio value purely by taking the mid-point of bid and asks. If you trade illiquid futures, IB is a ticking bomb! There is simply no way one could be expected to provide for an excess liquidity that reflects the kind of intraday price movements reflected by their method of calculation, which is completely prone to manipulation by low bids.