As a consequence of the distinct tendency of each group of orbitals toward a given d -occupancy, when a balanced set of weights is used the usual SA-CASSCF is prone to converge each set of the orbitals biased towards one occupancy, what ends up canceling out the bias. To exemplify this, we have shown that varying the SA-CASSCF weights for the copper subsystems tends to converge 3d -orbitals suitable to the d 10 -occupancy and the ligands orbitals to the d 9 -occupancy. For a better control of the orbital optimization we proposed to partially fix the reference space and optimize the orbitals in steps. Using this procedure we are able to optimize the ligand and metal orbitals in a way that both are intermediate for both occupancies and not an orbital bias cancellation error.