My condolences to the people with negative account balances. You may have screwed up to an extent in having too large of a position but I still feel badly for you.
My rule with the futures is to always assume that I am liable for the full contract value with my positions; I think Black Swan, which means I am trading futures less now and typically use the TQQQ and UPRO ETF's instead, scaling in and out. When I do trade futures, I trade mostly the NQ and ES indexes and periodically write the CME requesting either a micro-mini version of those or a "split" of the value per contract.
With Interactive Brokers, I was never very comfortable with their business model, which is, lots of active and leveraged traders of size, in the same boat, with dirt cheap equity margin also. If the market gets too stormy, the boat has a greater chance of going under, compared to a stodgy Broker like Fidelity (no futures though) or TDAmer/TOS. Yes, there are the commissions, product offerings and solid uptime/data and payouts at IB but those are no longer the driving force in my brokerage choice.
This currency mini-crash is a small example of my larger fear at IB which yes, "probably" will not happen.
So I was never very comfortable having much of my capital over there and combined with a recent reversion of their customer service back to "bad" (which indicates some kind of management problem to me), I am pulling the plug on all accounts there. GL.