In a previous publication (Tsiganis et al. 2000, Icarus 146, 240-252), we argued that the occurrence of stable chaos in the 12/7 mean motion resonance with Jupiter is related to the fact that there do not exist families of periodic orbits in the planar elliptic restricted problem and in the 3-D circular problem corresponding to this resonance. In the present paper we show that nonexistence of resonant periodic orbits, both for the planar and for the 3-D problem, also occurs in other jovian resonances-namely the 11/4, 22/9, 13/6, and 18/7-where cases of real asteroids on stable-chaotic orbits have been identified. This property may provide a "protection mechanism," leading to semiconfinement of chaotic orbits and extremely slow migration in the space of proper elements, so that diffusion is practically unrelated to the value of the Lyapunov time, T L , of chaotic orbits. However, we show that, in more complicated dynamical models, the long-term evolution of chaotic orbits initiated in the vicinity of these resonances may also be governed by secular resonances. Finally, we find that stable-chaotic orbits have a characteristic spectrum of autocorrelation times: for the action conjugate to the critical argument the autocorrelation time is of the order of the Lyapunov time, while for the eccentricity-and inclinationrelated actions the autocorrelation time may be longer than 10 3 T L . This behavior is consistent with the trajectory being sticky around a manifold of lower-than-full dimensionality in phase space (e.g., a 4-D submanifold of the 5-D energy manifold in a three-degrees-offreedom autonomus Hamiltonian system) and reflects the inability of these "flawed" resonances to modify secular motion significantly, at least for times of the order of 200 Myr.