From memory, I think QF takes a stricter view about duplicates than BA does (or, at least, used to take). ISTR at least one thread on the QF board saying that if you reserve more than one seat on the same route on the same day, QF will regard that as a duplication and cancel one of the bookings, even if the reservations are on different flights and even if both reservations are ticketed.
If one of the QF experts sees this thread, it might be useful to know whether that policy is still in operation.