Maryland Family Law Section 9-303

      (a)      This section applies if there is a conflict between a custody order of a court of this State and a custody order of a court of another state.

      (b)      Except as provided in subsection (c) of this section, a custody order of a court of this State prevails over a custody order of a court of another state.

      (c)      A custody order of a court of another state prevails over a custody order of a court of this State if the court in the other state passed its custody order:

            (1)      after the custody order was passed by a court of this State; and

            (2)      in proceedings in which the lawful custodian under the custody order of a court of this State:

                  (i)      consented to the custody order passed by the court of the other state; or

                  (ii)      participated personally as a party.