I fucking HATE that shit, I still remember it like yesterday when the CME gave a "warning" during the previous couple of weeks to all the desks that it could go negative, but on April 20th 2020 when it actually DID settle negative, they still had on their website the limit down breaker of $0.01. Mother fuckers, they fucked everyone on that bit. They are culpable, man.
IBKR had a flawed system, didn't handle negatives... and traders were fucked. That's why IBKR forgave the negative values of the trades, but still made clients pay for their loses that were on the positive side of the chart up to that point.
Negative? If they pay me to hold crypto, I would take them all, clear out the house. They are lightweight too, nothing like an oil delivery.