The pulses development dynamics, including their bifurcation into two-pulse complexes, was investigated in ring semiconductor lasers with amplitude modulation, operating on harmonics. New unusual properties of active mode-locking were revealed. They indicate significantly different dynamics of lasers operating on the first harmonic and those operating on any higher harmonic. The domain of control parameters for single pulses of higher harmonics is split into two domains: the dynamic boundary layer of finite width adjacent to the bifurcation line and the domain of dynamic chaos. Such layers engender stable dynamic sync-bands. We found conditions to implement energy-efficient sync-bands with optimum pulse parameters.