Although a lot of experimental and model results for roughness evolution exhibit anomalous scaling, the origins of such a behavior remain still unclear. In this paper, the possible contribution of material inhomogeneities to the appearance of anomalous scaling behavior in kinetic roughening is investigated by a simple modeling of roughness evolution in the etching of porous and composite films. It is found that the roughness evolution during the etching of both kinds of inhomogeneous films displays anomalous scaling behavior with peculiar features (no expansion of correlations vs time and square-root time increase in surface width roughness) defining a new universality class. Furthermore, the insertion of correlations between film pores or fillers along etching direction leads to roughness instability, i.e., linear increase in surface width roughness. The latter observation may be exploited for the detection of correlations between pores or fillers using roughness evolution as a diagnostic tool.