I am not an attorney but I stayed in a...well that is a lie I was at home, but.
The court which has jurisdiction in your case applied the law of THAT state and cares not, nor should they the laws of another state. VA doesn't give a rats ass about MD law even if one of the parents moved there, nor can they since VA courts have no jurisdiction nor do they have authority to enforce another states laws.
In most states, unknown if Maryland is one if you have primary physical custody (Custodial parent) you maintain the primary residence, utilities and responsibility for primary care, feeding and clothing. CS is calculated on combined income, - children from previous relationships and proportioned according to the ratio of income. Special consideration is given when the time spent with the NCP exceeds a preset amount of time. In some cases 100 days. the CS calculation takes into account not only the physical custodians responsibility for establishing a primary residence but visitation with the NCP.
In the end I agree while the child is with the NCP for extended periods IE: 8 weeks, CS payments to the CP should be suspended, but I would not go so far as to say the CS payment should be reversed. You see you are basing NCP and CP status on time spent whereas the court is establishing a responsibility for a primary residence.