Island formation in CdSe/ZnSe superlattice (SL) structures with a moderate defect density is investigated in a sub-monolayer range of CdSe nominal thicknesses. Besides the spontaneous formation of CdSe-enriched islands in defect-free regions, presence of dislocations crossing the SL causes an emergence of the defect-attached islands. The island location near interceptions of CdSe sheets with the dislocations produces a staircase ordering of the islands in neighboring SL layers. Such a mutual alignment of the CdSe-enriched islands results in modified optical properties of the defect-containing structures. Density and type of the defects promoting the laterally inhomogeneous incorporation of Cd are controlled, in general, by the initial stage of MBE growth and a lattice mismatch between ZnS(Be)Se cladding layers and a GaAs substrate.