Note that when you attach multiple child orders, IB may place limitations on the possible combinations of allowed child-order parameters. For example, when you add a MOC exit order to the standard bracket child-orders, IB only allows the child orders to have an OCA type of 3 (Reduce on fill without block) and not 1 (Cancel on fill with block) or 2 (Reduce on fill with block). Without the extra MOC child order, you could have your child bracket orders also use OCA Types 2 & 3, not just 1. Such limitations may depend on your specific secType and exchange.
Yair Altman