It was observed that in HxNbVO5 with x similar or equal to 1.4, the V-51 and Nb-93 high resolution solid state NMR lines (center transitions) are practically unchanged (chemical shift and line width) with respect to those observed in NbVO5. From thermodynamic data, the extent of the charge transfer from the intercalated H to the host lattice appears to be total in both HxNbVO5 and isostructural HxTaVO5. Hence, the formal oxidation state of vanadium in the bronze should be V-3.5+ and the abundance of V4+ and V3+ paramagnetic centers should prevent the observation of the V-51 (and Nb-93) resonances. A similar effect was reported earlier for HxV2O5. The NMR results are difficult to explain in the hypothesis, supported by the thermodynamic data of a complete charge transfer unless some electron-pairing occurs. Solving this problem raises an interesting a challenge which would undoubtedly require other techniques of investigation.