Actually IB, like most all brokers has a good bit of discretion when it comes to margin calls
yep. that would be my biggest concern. they done that in the past so many times. sometimes for no apparent reason. imagine situation,where they raise margin requirements overnight and if you are too tight-there is will be forced AUTO liquidation. this thing would be beyond your (and IB regular customer service control). they will just dump your shares on the market regardless.