Dimensions of cylindrical domains and microphase separation behavior in thin films of polystyrene-b-polybutadiene diblock copolymer (SB) are analyzed under fine variation of the surface fields, polymer-polymer interactions, film thickness, and the symmetry of the wetting conditions. In thermally and in solvent annealed films the dimensions of the closest to the substrate cylinders are smaller than both in thicker films and in bulk due to the confinement effect. The related excess of the stretching energy favors a transition to nonbulk perforated lamella morphology in a narrow window of the film thickness, solvent concentration, and annealing temperature. The discussion of the apparent stability/instability of thin film morphologies includes the analysis of molecular architecture, interfacial tensions, and possible influence of dynamic effects.