Two independent measurements of excitation functions in dissipative collisions of 19 F+ 93 Nb have been carried out at incident energies from 100 MeV to 108 MeV in steps of 250 keV. The experimental conditions were kept to be identical in both measurements. The data indicate non reproducibility of the non self averaging oscillating cross sections. The quasi periodic structure in the energy autocorrelation functions is described by means of the concept of parity and spin decoherence in the inter...