Abstract: The nuclear properties of bismuth isotopes (Z = 83), with just one valence proton above the closed spherical shell at Z = 82, are expected to be governed by a single unpaired proton. However, already in semimagic 209Bi (Z = 83, N = 126), the magnetic moment (mu) strongly deviates from the single-particle Schmidt value. A near linear decrease in μwith the increase of N after the N = 126 magic number was observed up to N = 130. In order to test whether this trend is kept at N> 130 and to reveal the underlying mechanisms, an investigation of Bi-215,Bi-217 (N = 132, 134) has been undertaken. The magnetic dipole and electric quadrupole moments of the I-x= 9/2-nuclear ground states in these isotopes have been measured for the first time using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). It has been shown that the linearly decreasing trend of mu(Bi-209,211,213(g)) is broken in Bi-215,Bi-217 with a nearly constant value of μobserved. Experimental data have been compared to calculations in the framework of the configuration-interaction shell model with the monopole-based universal VMU+LS interaction. The peculiarities in the behavior of μ(Bi, 9/2-) with increasing neutron number are explained as being due to the shell evolution, change of the neutron orbitals occupancies and strong configuration mixing beyond N = 130. Also, the difference in the μtrends for bismuth (Z = 83) and astatine (Z = 85) isotopes with N> 126 are reproduced by the shell-model calculations. It is shown that monopole interaction plays noticeable role in the description of the peculiarities of the μbehaviour. Additionally, the extension of the application of the V-MU interaction to the μisotopic trends for heavy nuclei is important for further study of the capabilities of this promising version of the shell-model calculations.