Remote observations of the Io plasma totus have revealed a persistent longitudinal asymmetry in the brightness of optical S+ emission lines but not of ultraviolet S++ emission lines. The S+ asymmetry (with respect to the corotating System III coordinates) has been attributed to an asymmetric plasma source; the question then arises, why do the higher ionization states of sulfur not reflect a similar asymmetry? The explanation proposed here is based on the fact that torus ions do not quite corotate at the System III rate because of mass loading. If the resulting System III drift period of the ions is intermediate between the ionization lifetimes of S+ and S++, then the asymmetry of the source will be obscured by longitudinal drift for the relatively long-lived multiply-ionized sulfur ions, but not for the short-lived S+.