This is a very important (and dangerous) aspect of holding an account with IB. Here is just one example (there are tons if one is interested in looking at their arbitration history) where a client got totally screwed, IB claimed no responsibility and was brought to arbitration (which costs the customer a ton of money). IB of course lost, but that has not stopped them from continuing the exact same practices today (and continuing to deny responsibility). Practices that they have been recently fined for by FINRA, the regulators in the UK, Hong Kong, and Australia.
https://www.reuters.com/article/us-arbitration-interactive-auto-liquidat/interactive-brokers-must-pay-667000-for-portfolio-selloff-mishap-panel-idUSKBN0LM23620150218