Nothing you claim is stated in that document you linked and as someone who has done a great deal of business with IBKR for the better part of 15 years now as we

Nothing you claim is stated in that document you linked and as someone who has done a great deal of business with IBKR for the better part of 15 years now as well as one of the largest market makers on the Australian markets making up approximately 5% of all ASX and CHIX volume, I assure you there absolutely no protection provided to a client whose balance enters into a negative position. Clause 3.A.e specifically states that trading on margin can result in a loss of funds greater than that deposited into your account and that you accept that risk. In conjunction with Clause 7.K which states that you must reimburse the broker for any liabilities as a result of the liquidation undertaken by the broker. You are always on the hook for the full amount of losses on margin.