Just because it is split 50/50 doesn't mean anything. They could still be fares with a roundtrip booking requirement and you just got the same roundtrip fare for both outbound and return flights. You still have a fare in each direction with roundtrip fares. They just have a roundtrip booking requirement as part of the requirement to book them. Without knowing route, can't really determine much here. There's also a chance they will reprice the outbound flight when just cancelling return even if they are one-way fares (it depends on the fare rules -- AA domestic rules look to be more liberal for keeping original fare when changing return before departure). If it's a route with only one-way fares, it can often be better to book them as two one-way's instead of a roundtrip for this reason if you think you might change one flight or the other.