In some solar energetic particle events relatively intense proton fluxes are accompanied by disproportionately weak intensity ofμ-burst. A possible reason for such a situation is discussed in this paper. We use the idea that the dynamics of particles in flare loops strongly influences the efficiency of their escape into interplanetary space. It is proposed that in events with weak impulsive phase flare loops are large sized and stretched high into the corona, the magnetic field is weak, and the level of excited turbulence is rather low. All this leads to the weak diffusion of protons into the loss cone, a large lifetime of a particle in the loop (≈ 103 s) and, hence, to the relatively high efficiency of their escape into interplanetary space.