Description: This article discusses Z1 oscillations of the mean charge for isotachic ions in carbon foils. Oscillations in the mean-charge state of swift ions as a function of the atomic number Z1 are reported for a wide range of ions of identical velocity (isotachic ions). A previously suggested mechanism for the enhancement of the mean charge for certain ion-charge combinations that involves closed shells is shown to be an inadequate explanation. Post-foil-Auger processes, however, are demonstrated to be a more plausible explanation for the observed behavior of the mean charge of the ions.