I mean that they can take a long time to actually process the payment. Basically when you go to buy something it takes a few days for the transaction to go through, so the bank just sets aside the funds for the authorized amount but it's not technically paid. For whatever reason IB can take weeks to get the payment through. There's a decent chance IB is actually paid as well from their payment processor and it's just taking some time to get withdrawn from your account.

Just make sure you have the funds available to be debited at any point, but hey....bank errors can and do happen so I wouldn't have them looking too closely at it.