A polymer electrolyte system composed of poly(propylene oxide) of molecular weight 4000 (PPO4000) complexed with NH4CF3SO3 (NH4TF) has been investigated by multinuclear pfg-NMR and AC impedance methods. Samples in the concentration range 0.03-0.69 mol/kg (O:NH4 ratios of 500:1-22:1) have been investigated over the temperature range 25-75 degreesC. The combination of AC conductance and pfg-NMR diffusion measurements gives clear evidence that extensive ion-aggregation/clustering occurs at low salt concentrations. With increasing salt-content the Haven ratio, defined as Lambda (calc)/Lambda (exp), decreases from >100 to similar to2 when going from 0.03 to 0.69 mol/kg. Such gross deviations from the Nernst-Einstein relation (i.e. Lambda proportional toD(+) + D-) originate in extensively correlated motions of ions. We interpret the results in terms of labile salt-rich sub-domains being further destabilized through an increase in the dielectric constant of the solution with increasing salt content.