(a) Substitution for military leave.--When an employee in the classified service is granted military leave, the position vacated shall be filled only by substitute appointment or promotion and the employee appointed or promoted shall vacate the position upon return of the employee from military leave. A substitute employee, when required to vacate a position upon the return of the regular employee, shall have the right to return to the substitute employee's previous civil service position and status.

(b) Substitute lists.--The substitute appointment or promotion shall be made from lists certified by the Office of Administration under this chapter.