Flying business LHR - LAX and need to change to LHR - JFK - LAX. On AA.com, when I reprice the ticket, I get a marginal fare difference as both LHR - JFK and JFK - LAX book into to I. But when I call the EXP desk to make the change, the fare difference is large, as LHR - JFK goes into I but JFK - LAX goes into D or J (depending on the flight).

Anyone know what's going on here? EF is showing I avaliable on all legs too.