Within the framework of the periodic bond chain analysis for the prediction of crystal morphology, connected nets play a crucial role. For a face (hkl) often more than one connected net is found. Symmetry relations between such connected nets can give rise to symmetry roughening of nets. In this paper, all cases where symmetry may lead to symmetry roughening are derived. The role of a mother phase in contact with the crystal is explicitly taken into account. It turns out that cases of symmetry roughening are, in a sense, complementary to situations where the classical Bravais-Friedel-Donnay-Harker selection rules apply.