While you are correct in that, how many Convairs are listed as General Dynamics? Or Martins as Lockheeds?
I think that they'll change their minds in the books. However, the fact is, Boeing owns MDD, and so MDD aircraft are technically Boeings.
AirTran has an all Boeing fleet, in the manner described by others. The Ryan International planes were just a wet-lease, in the same manner than NJ
wet-leased 727s from TransMeridian. The difference is that the A320s are painted in Ryan colors, while the 727s were always in TransMeridian colors. Other, similar leases go on all the time.
Those who fail to learn history are doomed to repeat it in summer school.